How many times has the WTBTS told people to 'count the cost', giving the example of someone wanting to build something and coming up short in the middle of it all and look like a fool when they couldn't finish what they started? This is an example of the local elders NOT checking everything out and getting caught. If they had checked everything out, and knew about the alcohol ban, they then exempted themselves from the ban's application.
The other church uses fake wine, and remain in compliance, the building managers could not overlook the fact that the ban needs to be enforced fairly. Perhaps the designated security for the building couldn't be on hand because of previous engagements.