The handling companies can hardly manage to tell their aircraft about their slot times
Throwadyce this problem is not confined to ABZ. At most of the UK airports I have operated from I remember occasions where ATC have told us we have a slot just after our request for pushback. On subsequently cancelling the pushback request we call our handling agents for verification only to find they still have no information about any slot.
It would seem ATC's communication link with Brussels is much speedier than the SITA or whatever system handlers use. This has been going on for years and I don't think it is a case of handling companies "hardly managing".