Yeah, notwithstanding the other snarky posts, I can see why you are confused. Here are the facts as I see them:
Limited Production - this means something specific in the way folks are using the term. Porsche produces cars (ex. 991R, Speedster, 997 RS 4.0, Turbo Exclusive, etc.) that are actually numbered. These cars are generally very hard to come by both new and used. Some have been truly exceptional (997 RS 4.0, 991R, etc.)
Allocations - basically all Porsche cars have allocations. Regardless of what anyone says, Porsche doesn't make as many GT cars as people want. They have limited production capacity and they only produce a given GT variant for a period of time thus there is a "limited" number of new cars. This number is typically higher than the number of cars they produce for a limited production car like the 991R. If one wants to configure their own GT car, they need to secure an allocation from a dealer and the total number of allocations available is relatively fixed. For the most part the dealers control the distribution of the allocations and the games begin there.

Moving from facts to my take - The decision to pay or not pay an ADM is a personal one. I respect those who advocate patience and also those who are willing to "miss out" on a GT car and consider options from other manufacturers. From my experience there is no guarantee that by waiting until later in the run that one will get a GT car w/o an ADM. Some will, some won't. In the case of the 991.2 the GT3 remained relatively tough to get through the whole run but the 991.2 3RS was a bit less so by the end of its run. Again my opinion only - it will take luck on top of patience to get a late allocation w/o an ADM. It will for sure happen for some but I doubt for all those who want cars. Kind of like musical chairs - some people will be left standing.