Are rented units not intended to "serve additional households"?
Are non-rented units not intended to serve the current household?
The POINT is the city makes no mention of if its Rented or not Rented as to if it is a Dwelling Unit in there eyes.
So, your buddy's basement was stipped to remove the kitchen, rightly or wrongly-depends how your buddy handled the situation.
I still do not see the great hand wringing over this issue. You and A. L. seem so concerned, your choice-which I don't agree with but also don't have a proble with it- why not just call every 2nd or additional kitchen over the zoning allowance as illegal and treat it accordingly?
I'd be very careful with that stance, I have several properties with the additional kitchen in the lower level with the City's blessing, some have even been given a Zoning Cert indicating the 3rd unit as legal.-
If the city has determined it to be Legal then it is Legal, it's not what I posted originally but thats OK
I would hate for some appraiser to call out my kitchens as illegal when they are not.
The OP asked how people handle these situations, Lee and I have offered our method, you don't seem to like it.