Responsibility for damage to grammar

On Sunday we took a trip to the Showcase cinema at Foresters Park in Derby. This is itself a bit of a punctuation grey area - was there more than one forester, in which case it should be Foresters'? Or was there only one, in which case Forester's? Or - final option - was the park named after a Mr Foresters, in which case well done Derby City Council? (This is my internal narrative. This sort of thing goes on in my head ALL THE TIME.)

Anyway - the cinema and environs proved to be a veritable goldmine of dodgy grammar and punctuation. This first one was on the wall outside the building before we even got into the foyer.

Now, last time I checked, the management used in this context is a singular noun, referring to a group of people as a unit. Therefore, the wording on the sign should be The management does not accept responsibility yada yada. If they'd said the managers instead, their version would have been correct. BUT THEY DIDN'T.

Since I'm here, I'd also take issue with their use of whilst. Although it's technically correct, it's an archaism which should probably be allowed to die a quiet and dignified death along with amidst, amongst and unbeknownst. However, I'll let them off that one. Just this once.

By the way, in case anyone's wondering, we saw Avengers Assemble, and it was very silly and utterly splendid. There you go - who needs IMDb?