JJ,
Under the RAF system the ALM is (or was) obliged to accept the weights presented to him. The same can be said for the movers unless a means of checkweighing the load was available. Away from a main base this was seldom the case. The big danger was tac onloads at another NATO base where everyone used kgs but the UK and the USAF.
The Herc tanker regularly operated at weights well in excess of the normal TOW.
But this was planned as were several of the other Corporate excesses.
When the lbs/kg rule appeared in build up to GW1 I put a warning note in the section 'Do you know' book. This was mandatory for my troops to read and sign before they set off. There were no excuses for non compliance !