What is the difference between BEFORE, SENTBEFORE, and SAVEDBEFORE?

In doveadm-search-query(7), it states:

 BEFORE date specification
     Matches messages with an internal date before date 

specification.

 SENTBEFORE date specification
     Matches messages with a Date: header before date specification.

 SAVEDBEFORE date specification
     Matches messages, which were saved before date specification.

I am creating a cron job to purge old messages in Trash or Spam folders, but I discovered using doveadm search queries using savedbefore that somehow no message in any of the folders shows up with queries starting at 5d, even though there are much older messages.

doveadm search mailbox Trash before 90d -A | wc -l 277 doveadm search mailbox Trash sentbefore 90d -A | wc -l 277 doveadm search mailbox Trash savedbefore 90d -A | wc -l 0

For my purpose, I'm not clear on the differences between the different queries and am wondering what will be the better option.

Thank you,

Paul