So did mine until I was about to rent my flat and needed to show it to a lettings agency; I would have been a complete idiot to not have changed it (and one without a flat). Are you saying you would have left it?
We have countless posts from members here about the various occupations they have on theirs; I've never lied to a bank, but given the problems others have had I can understand why some would and I'm surprised if some people can't.
What documents did they ask to see please? This is news to me because I’ve never known anyone to request a full copy of a self assessment. They usually ask for SA302 and tax calculation/overview neither of which state your occupation. So in theory your self assessment can say Gardener and you could tell your bank Dog walker and they couldn’t check.
I did this when getting my mortgage. I told the mortgage a different occupation to what is on my self assessment and had no problems.
Same as when I got my car finance and a loan.
I’ve helped a couple of my friends too and they never had to show their full self assessment so no way of knowing the occupation