Perhaps the adjacent agencies were aware of the NOTAM but had no information on the actual status of the drop. Therefore they could offer 'no information' to let the pilot know whether it had been completed or not ??
The exercise sponsors should be aware of the need to issue a cancellation NOTAM once the airspace was no longer needed by them, in these days of Flexible Use of Airspace and sharing. Sadly, some MoD units are much better than others at doing so.