Offering price reductions without a corresponding reduction in scope is the same as saying you were overpriced to begin with.
Well yes... perhaps; it all depends on the starting point. When TETRA / Airwave rolled out there will have been a significant part of the cost allocated to amortising the costs of site acquisition and mast / building construction. It seems unlikely that the payments allocated to paying off those costs would be based on a assumption that the contract would be extended at all, never mind for as long as it has been so far.
I don't know for sure either way, but Motorola should have been able to reduce the annual charges paid by the Taxpayer because all the initial expenditure had been covered, with "just" maintenance costs chargeable thereafter.
On the face of it Motorola ought to be been able to offer a reduction some years ago, even allowing for the fact that some of the electronics might have to be replaced, but I strongly suspect that they didn't.
Would the "corporate you" if you thought you could get away with it?