ACM-Reference-Format produces incorrect journal month and year

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Background

Several BibTeX citations provided by the ACM Digital Library have a fundamental error in how they handle month and year. A key example is POPL 2020 (Proc ACM Program Lang, Volume 4, Issue POPL). The papers were published online in December 2019 but the issue itself is dated January 2020.

As a result, the ACM provide the following incorrect BibTeX (e.g., the first paper).

@article{10.1145/3371069,
author     = {Barbarossa, Davide and Manzonetto, Giulio},
title      = {Taylor subsumes Scott, Berry, Kahn and Plotkin},
year       = {2019},
issue_date = {January 2020},
publisher  = {Association for Computing Machinery},
address    = {New York, NY, USA},
volume     = {4},
number     = {POPL},
url        = {https://doi.org/10.1145/3371069},
doi        = {10.1145/3371069},
journal    = {Proc. ACM Program. Lang.},
month      = {dec},
articleno  = {1},
numpages   = {23},
keywords   = {Taylor expansion, Linear Logic, Lambda calculus, B\"{o}hm trees}
}

The month and year are referring to the date the paper was available online, whereas issue_date refers to the date of the journal proceedings. This design is a mistake, because the issue_date field is not recognized in any known bib format, producing errors even with the offical ACM-Reference-Format.bib format.

For the above article, the ACM Reference Format shown on the first page is

However, the actual citation generated using ACM-Reference-Format.bib is

It contains the wrong month/year for the journal (POPL, Article 1 (dec 2019)). This result is in direct contradiction with the official ACM Reference Format printed on the very article itself.

Solutions

There are several solutions:

• Solution A: The bib files provided on the ACM Digital Library should use month/year to refer to the journal month and year, which is consistent with the citation shown the article pages. If it is important o capture the online date in the bib file, issue_date should be replaced with online_date. This fix will solve the problem for any bib format.

• Solution B: ACM-Reference-Format.bst should use issue_date when available, instead of month and year. This fix will not generalize to other bib formats. Things also become trickier because the ACM's intention is unclear. For example this approach could also consider using year after the author names (for the online year) and issue_date in the journal date, giving:

Davide Barbarossa and Giulio Manzonetto. 2019. Taylor Subsumes Scott, Berry, Kahn and Plotkin. Proc. ACM
Program. Lang. 4, POPL, Article 1 (January 2020), 23 pages. https://doi.org/10.1145/3371069

(This design would be a use case for the need to render two year values, which many have noted is currently redundant e.g., #151; #432; #306; #200)

Addendum

There is another problem in the bib file. They write month = {dec} instead of month = dec, which renders as dec instead of Dec. or December.