How is weight gain or rather RATE of weight gain related to the NLP and the point at which this comes to an end?

For example, let's say someone is able to gain weight fast enough to support an NLP up to say a 350lb squat.

Someone else gains weight at a much slower rate (hardgainer) and only reaches 250lb. However, if he were to run the NLP in "slow motion", the rate of weight gain would be enough to support the NLP up to 350lb for the same person.

How do you deal with this situation? Do you just end your NLP at 250lb, or run it slower (there are various ways of achieving this) until you reach 350lb?

This brings me onto another question: what exactly is the NLP defined by? Is it simply defined by rate of progress? If so then that seems a bit superficial because I don't see why the hardgainer can't be said to be running an NLP, even if their rate of progress is slower. Their progress can be said to be identical to the first person's progress but just slower.