2 bedroom SFH converted to 3 bedroom risks

I see many older SFH 2 bedroom houses that have been converted to 3 bedroom houses eliminating the garage in most cases to do the conversion. So they end up going from a 2/2 or 2/1 to a 3/2 or 3/1.

Is there a risk to buying these types of SFH's with regards to permitting or anything else you can think of?