You are assuming that the original denial was "illegal." Since we have no idea of the nature of the complaint/allegation, there is no way to determine whether it was something that could still be an issue or might be grandfathered in.
As a note, in my city, they discovered that a great number of waivers were VERBALLY granted for work done on properties here. Unfortunately, those waivers were never documented anywhere by the then-building inspectors, and as a result they remain unlawful additions or modifications. And since the original inspector who allegedly issued these verbal waivers (which were not permitted even at the time) has since passed away a number of folks have found that work done is not permitted and has resulted in the devaluation of property or lack of insurance coverage after a claim for the affected area of the property.
But, we do nto know what the isue is as the OP has not provided that info.if there was a permit and the construction was given a final inspection and approval, that's it for the city. They don't get to revisit what they approved 30 years ago.
If the OP is not planning to sell or do any work, then the city will have no real grounds to pursue the matter ... unless the issue is a health and safety issue. We simply do not know.
Yeppirs!but given the paranoid statements of the OP, I suspect there is more to the issue than we are being told.



