There are a couple of issues here:
First, when purchasing a home, particularly with FHA financing, unpermitted work is going to cause a big problem. We have had illegal garage conversions make properties ineligible for FHA financing.
Second, IF the city of Glendale finds out, they can make the owner bring the property to code. There was a property last year that had an unpermitted garage conversion that included a full bath and kitchen removed prior to sale.
To find out what is and is not permitted, contact the Dept. of Building and Safety and has jurisdiction for the area and ask for copies of the building permits.