After the gang makes their first 'bad' cannon, they need to get it past the inspector. There is a cut to a front shot of the inspector, who is working on three cannons on his table. There is a cut to the inspector's table - shown from beside the inspector - but there are only two cannons on the table now.
The factory towers have flashing lights on them. Not a good idea in wartime.
In the establishing shot showing the outside of the "Hof Brau" restaurant, 1960's cars drive by.
Hogan indicates that the four factory workers that he and his men replaced are being held by the underground until Hogan contacts them after the operation is complete. There is no indication that the four men they replaced had families, but it would be a problem if they did, because the wives and other family members would have raised the alarm when their men did not come home. Also, since this plant is being re-tooled from manufacturing cars to manufacturing cannons, the assumption is that they would not have replaced all the workers, and that most of the original workers would have stayed on. in that case, the four workers that were replaced would almost certainly have been known to other workers at the factory, and those other workers would have noticed that the tags Hogan and his men are wearing do not match the real workers.
Hogan would never have requested a bombing run for a plant only one mile away from Stalag 13, due to the high possibility of a stray bomb hitting the Stalag.