Yes, if I set HISTFILESIZE to -1, then bash would maintain an unlimited history file

I wish I'd known that, I just keep making the number bigger!

The following doesn't help with the current problem, but: this will be a trivial problem in the future if you add HISTTIMEFORMAT='%Y%m%d-%H%M%S ' to ~/.bashrc, or to /etc/bash.bashrc. Then start a new terminal session and issue a few commands, then issue history | tail and you'll see what I mean. You'll have to do something like history | sort -k 2 | grep 'what you want to see', as somehow things are still out of sequence. I think that happens to me because I generally have 3 or more terminal windows open, doing things in each, and the history file gets written (I think) when the bash session ends,