Top Bunk,
Now I have a question. If I understood James Brake's original question, he wanted to know at what point the MEL ceases to be a legally-binding document for the operation/crew, saw this point as the moment at which you are "dispatched", and wanted a definition of "dispatched".
From your comments, did you mean you are no longer legally bound by MEL restrictions at first engine start/moving under own power ? So, you could ignore the mechanical discrepancy if it occurred during taxiout, for example, and takeoff with no further legal encumbrance because the problem appeared AFTER you had moved under your own power ?
I suspect we're comparing apples to apples more than it would appear. For us, the MEL is legally binding any time the acft is on the ground until "..the throttles are advanced...", as I quoted before. It isn't tied to a particular point of progress durng ground ops prior to that point.
Our particular MEL procedures are further complicated by "pilot placarding procedures" where the crew can legally inop some items without the services of a mechanic. The implementation of this twist is, in fact, tied to various points of progress while on the ground ( I won't bore you with those).