Clarify VDI-FIX compatibility

Fixes #86.

gem/vdi/control/v_opnvwk.ui

@@ -362,7 +362,8 @@ itseslf in the (!I)multiple(!i) assignation of IDs, and hence the workstation
 attributes may be misplaced in some circumstances. This error appears if there are
 (!I)gaps(!i) in the internal workstation list of the screen driver. Remedy: Place
 the patch-program (!B)VDIFIX(!b) in the AUTO folder. (!nl)
-The problem is also in TOS 2.06 and 3.00, but there is no patch.
+The error is present also on TOS 2.06 and on early (built before 31.05.1990) TOS
+3.00 builds. Unfortunately, no patch is available for those TOS versions.
 
 !item [(!nolink [Return]) value:]
 The function returns no direct result.