Hello, I see date processing is still in the pipes ! (See issues #1249 and #6224)

Almost two years ago (see here), I asked for a way to write a custom export with dates from the biblatex date field to bibtex year, month and day fields with an emphasis on the month field (I am not the first one, see here).
I tried using the DateFormatter but an error is still raised when the date field doesn't resolve as a full ISO date (YYYY-MM-DD), and even if it worked, it would only output the month number, and not the bibtex equivalent.

Any clue on how to solve this ?