Missing mail in trash?

I just went into my Trash folder in Mail to look for something and there's hardly any mail in there???!!! I should have hundreds or thousands of emails in there and I'm always searching through to find things. I tried a search for something and it showed up in a search but when I manually look in my trash it's not there, only the stuff I've deleted today. Other items I search for don't appear at all, like Amazon or eBay receipts, of which there should be loads going back to god knows when.

I have it setup so that all deleted mail goes to the Trash on my Mac and not on the server (iCloud) and it's setup to never delete any mail. I prefer to manually delete it once in a while when I can take out any emails I may need.

Please help 😟