If you're still looking for some convenient date magic, maybe try some variation of this:
Code:
date --date="yesterday" "+%Y%m%d"
date --date="2 day ago" "+%Y%m%d"
date --date="3 week ago" "+%Y%m%d"
etc with what you can probably guess for the keywords.
The "--date" argument with a relative "datestr"
should work with any moderately recent version of GNU date (not macOS's ancient BSD date).