I lost my Smart Mailboxes. I created a new one and it stays. Can I get them back?

I had 5 or 6 smart mailboxes set up which have disappeared. I read about others with this problem, but they say the issue is repeatable when they restart. I created a new smart mailbox and it stays after a restart.

I checked some of the threads and have tried the following:

I made sure it wasn't an issue with them being hidden. The new one I created shows.

I used spotlight to try to find the plist files, but can't find them to see if they exist. Not even the new smart mailbox shows up in a spotlight search.

I have tried to find the Mail folder or the MailData folder with no luck.

Mail itself seems to be working fine and the new smartmailbox is working fine.

Any way to get the old ones back? (I can recreate them easily enough, but want to understand the problem so I can prevent future occurrences)