For a long time, this library didn't specify any bounds at all on dependency versions. Unless these can be retroactively added, which would be a huge amount of work, I'd suggest deprecating old versions in order to prevent users getting bad build plans. What I'd actually probably do in this case is deprecate 1.13.0 and earlier, since there are no bounds there at all, then figure out the correct base bounds for 1.14.0 and 1.15.0, instead of < 5, and add these via Hackage revisions. This is similar to what I'm told the miso library is about to do for the same reasons.

One consequence of the current situation is that a user with GHC 9.10 ends up building discord-haskell-1.15.1 because Cabal sees it as the most recent version which supports base-4.20. See also this Reddit thread.