Throughout the run of the series, Hooker has destroyed his cruiser at least a dozen times, but when he gets a new cruiser, it's always serial number 49357. Once a cruiser is destroyed, the serial number would not be reused.
When Romano is going after the sniper and tackles him on the roof, it is a stunt double that does the tackle. When the camera cuts, it is Romano again.
Soon after the start of the episode Hooker called his squad to 'Attention!' and the sound of army boots coming together on a hard parade ground could be heard. However when a wide shot of the group was shown they were wearing (male and female) civilian shoes and standing on soft grass.
At the deli shooting scene when the patrol car pulls up, you can see a real LAPD cop directing traffic around the shooting scene with cones.
TJ's police department was in California but, the scene showing TJ drinking with the recruits in the Tin Palace was clearly in New York.