diff --git a/asdf/_block/manager.py b/asdf/_block/manager.py
index 99c4bf957..dca8f94c5 100644
--- a/asdf/_block/manager.py
+++ b/asdf/_block/manager.py
@@ -1,3 +1,4 @@
+import collections
 import contextlib
 import copy
 
@@ -10,23 +11,15 @@
 from .options import Options
 
 
-class ReadBlocks(store.LinearStore):
-    """
-    {obj: block_index} : where obj is NDArrayType or other high level object
-    [block_0, block_1, ...]
-    """
-
-    def set_blocks(self, blocks):
-        self._items = blocks
-
-    def append_block(self, block):
-        self._items.append(block)
+class ReadBlocks(collections.UserList):
+    # workaround inability to weakref a list
+    pass
 
 
 class OptionsStore(store.Store):
     """
-    {array_base: options}
-    read_blocks (instance of ReadBlocks)
+    A Store of Options that can be accessed by Key
+    (see ``asdf._block.store.Store``).
     """
 
     def __init__(self, read_blocks=None):
@@ -34,10 +27,45 @@ def __init__(self, read_blocks=None):
         self._read_blocks = read_blocks
 
     def has_options(self, array):
+        """
+        Check of Options have been defined for this array
+        without falling back to generating Options from
+        a ReadBlock.
+
+        Parameters
+        ----------
+        array : ndarray
+            The base of this array (see `asdf.util.get_array_base`) will
+            be used to lookup any Options in the Store.
+
+        Returns
+        -------
+        has_options : bool
+            True if Options were previously defined for this array.
+        """
         base = util.get_array_base(array)
         return self.lookup_by_object(base) is not None
 
     def get_options_from_block(self, array):
+        """
+        Get Options for some array using only settings read from a
+        corresponding ReadBlock (one that shares the same base array).
+        Any Options defined using previous calls to set_options will
+        be ignored (use ``get_options`` if you would like these previously
+        set options to be considered).
+
+        Parameters
+        ----------
+        array : ndarray
+            The base of this array (see `asdf.util.get_array_base`) will
+            be used to lookup a corresponding ReadBlock.
+
+        Returns
+        -------
+        options : Options or None
+            Options initialized from settings read from a ReadBlock
+            or None if no corresponding block was found.
+        """
         base = util.get_array_base(array)
         # look up by block with matching _data
         for block in self._read_blocks:
@@ -52,6 +80,27 @@ def get_options_from_block(self, array):
         return None
 
     def get_options(self, array):
+        """
+        Get Options for some array using either previously defined
+        options (as set by ``set_options``) or settings read from a
+        corresponding ReadBlock (one that shares the same base array).
+
+        Note that if no options are found in the Store and options
+        are found from a ReadBlock the resulting Options will be added
+        to the Store.
+
+        Parameters
+        ----------
+        array : ndarray
+            The base of this array (see `asdf.util.get_array_base`) will
+            be used to lookup any Options in the Store.
+
+        Returns
+        -------
+        options : Options or None
+            Options read from the Store or ReadBlocks or None if
+            no options were found.
+        """
         base = util.get_array_base(array)
         options = self.lookup_by_object(base)
         if options is None:
@@ -64,6 +113,23 @@ def get_options(self, array):
         return options
 
     def set_options(self, array, options):
+        """
+        Set Options for an array.
+
+        Parameters
+        ----------
+        array : ndarray
+            The base of this array (see `asdf.util.get_array_base`) will
+            be used to add options to the Store.
+
+        options : Options
+            The Options to add to the Store for this array.
+
+        Raises
+        ------
+        ValueError
+            If more than one block is set as a streamed block.
+        """
         if options.storage_type == "streamed":
             for oid, by_key in self._by_id.items():
                 for key, opt in by_key.items():
@@ -78,6 +144,15 @@ def set_options(self, array, options):
         self.assign_object(base, options)
 
     def get_output_compressions(self):
+        """
+        Get all output compression types used for this Store of
+        Options.
+
+        Returns
+        -------
+        compressions : list of bytes
+            List of 4 byte compression labels used for this OptionsStore.
+        """
         compressions = set()
         cfg = config.get_config()
         if cfg.all_array_compression == "input":
@@ -96,26 +171,57 @@ def get_output_compressions(self):
 
 
 class Manager:
+    """
+    Manager for reading, writing and storing options for ASDF blocks.
+    """
+
     def __init__(self, read_blocks=None, uri=None, lazy_load=False, memmap=False, validate_checksums=False):
         if read_blocks is None:
             read_blocks = ReadBlocks([])
         self.options = OptionsStore(read_blocks)
-        self.blocks = read_blocks
+
+        self._blocks = read_blocks
+        self._external_block_cache = external.ExternalBlockCache()
         self._data_callbacks = store.Store()
+
         self._write_blocks = store.LinearStore()
         self._external_write_blocks = []
         self._streamed_write_block = None
         self._streamed_obj_keys = set()
         self._write_fd = None
+
         self._uri = uri
-        self._external_block_cache = external.ExternalBlockCache()
+
+        # general block settings
         self._lazy_load = lazy_load
         self._memmap = memmap
         self._validate_checksums = validate_checksums
 
+    @property
+    def blocks(self):
+        """
+        Get any ReadBlocks that were read from an ASDF file
+
+        Returns
+        -------
+        read_blocks : list of ReadBlock
+            List of ReadBlock instances created during a call to read
+            or update.
+        """
+        return self._blocks
+
+    @blocks.setter
+    def blocks(self, new_blocks):
+        if not isinstance(new_blocks, ReadBlocks):
+            new_blocks = ReadBlocks(new_blocks)
+        self._blocks = new_blocks
+        # we propagate these blocks to options so that
+        # options lookups can fallback to the new read blocks
+        self.options._read_blocks = new_blocks
+
     def read(self, fd, after_magic=False):
-        self.blocks.set_blocks(
-            reader.read_blocks(fd, self._memmap, self._lazy_load, self._validate_checksums, after_magic=after_magic)
+        self.blocks = reader.read_blocks(
+            fd, self._memmap, self._lazy_load, self._validate_checksums, after_magic=after_magic
         )
 
     def _load_external(self, uri):
@@ -325,7 +431,7 @@ def update(self, new_tree_size, pad_blocks, include_block_index):
 
                 # we have to be lazy here as any current memmap is invalid
                 new_read_block = reader.ReadBlock(offset + 4, self._write_fd, self._memmap, True, False, header=header)
-                new_read_blocks.append_block(new_read_block)
+                new_read_blocks.append(new_read_block)
                 new_index = len(new_read_blocks) - 1
 
                 # update all callbacks
@@ -334,7 +440,6 @@ def update(self, new_tree_size, pad_blocks, include_block_index):
                     if obj is None:
                         # this object no longer exists so don't both assigning it
                         continue
-                    new_read_blocks.assign_object(obj, new_read_block)
 
                     # update data callbacks to point to new block
                     cb = self._data_callbacks.lookup_by_object(obj)
@@ -343,4 +448,3 @@ def update(self, new_tree_size, pad_blocks, include_block_index):
 
             # update read blocks to reflect new state
             self.blocks = new_read_blocks
-            self.options._read_blocks = new_read_blocks
diff --git a/asdf/_serialization_context.py b/asdf/_serialization_context.py
index a31d3c59f..0925d04be 100644
--- a/asdf/_serialization_context.py
+++ b/asdf/_serialization_context.py
@@ -207,15 +207,13 @@ class _Deserialization(_Operation):
     def __init__(self, ctx):
         super().__init__(ctx)
         self._obj = None
-        self._blk = None
         self._cb = None
         self._keys_to_assign = {}
 
     def __exit__(self, exc_type, exc_value, traceback):
         if exc_type is not None:
             return
-        if self._blk is not None:
-            self._blocks.blocks.assign_object(self._obj, self._blk)
+        if self._cb is not None:
             self._blocks._data_callbacks.assign_object(self._obj, self._cb)
         for key, cb in self._keys_to_assign.items():
             if cb is None:
@@ -227,21 +225,15 @@ def __exit__(self, exc_type, exc_value, traceback):
             # assign the key to the callback
             self._blocks._data_callbacks.assign_object(key, cb)
 
-            # and the block
-            blk = self._blocks.blocks[cb._index]
-            self._blocks.blocks.assign_object(key, blk)
-
     def get_block_data_callback(self, index, key=None):
-        blk = self._blocks.blocks[index]
         if key is None:
-            if blk is self._blk:
-                # return callback for a previously access block
-                return self._cb
-            if self._blk is not None:
-                # for attempts to access a second block without a key
+            if self._cb is not None:
+                # this operation has already accessed a block without using
+                # a key so check if the same index was accessed
+                if self._cb._index == index:
+                    return self._cb
                 msg = "Converters accessing >1 block must provide a key for each block"
                 raise OSError(msg)
-            self._blk = blk
             self._cb = self._blocks._get_data_callback(index)
             return self._cb