It seems this bibliography style is not properly maintained or does not support certain commands to cite year and author separately. A warning is issued indicating there is no year available in the bibliography entry (although there is) and the text is replaced with author?.
Any idea how can I create a command to replicate the citeyear behaviour?
Example:
Warning I'm getting is:
Package natbib Warning: Author undefined for citation `paperA' on page 6 on input line 339.
Then the output looks like:

biblatexstylenaturehere, and moving away from 'classical' BibTeX if you can. (Note: I am the author of that style.) – Joseph Wright Sep 29 '20 at 18:07