Parking in Alley's

Parking in Norristown's Alley's is supposed to be a fire code violation, I understand that, so why when my SIL parked in the alley behind Tyler St. (Tauber Alley) he was issued a parking ticket. Yet there are people that park there all the time, they just never get caught. One neighbor even put a cinder block that she painted yellow and put her address on it with a sign saying Illegally cars towed by Pat's towing and yet this weekend she parked there all night and got no ticket .I'm not trying to make trouble but why can some people park there and some can't?