that would require sitting down and manually doing that for every conceivable payee

That's just called VLOOKUP(). I think you're over-complicating this process. If you sit down and look at your finances, you'll notice that the number of payees you have isn't some absurd unmanageable amount. As others have mentioned, there's no real use case for involving AI this way. There's no scale, no real benefit to financial tracking, etc. I get this is just to use AI for the sake of using AI, but that's not really a goal when writing financial software.