Are we notified anywhere when a DB entry previously approved is suddenly deleted (sometimes weeks or months later)?

No, I don't think so. DB entries are deleted when they're found to be duplicates, misspelled duplicates, synonyms, or invalid names, and these facts sometimes are not discovered for weeks or months. Any photos or comments attached to these entries are moved rather than being deleted, and the photo and comment contributors are notified of the move in those cases.

If you're concerned about a specific plant you added in the past, try searching for it to see whether it has been added to another entry as a synonym.

Thanks for the response.

I think we should be notified when deletions occur, if only to learn from mistakes.

I've invested a lot of time searching and entering new plants only to find totals drop inexplicably
Recently total topped 11000, now it's appx a hundred less.
.