I think TGC failed the collective test. Believe it or not, I was lurking when this was launched. At the time it was new so I went with it for a while. BPSFL is such a variable measurement and there are so many factors involved in getting accurate measurements; I don't think this theory has a reliable basis for determining what our limiting factors are. And I don't think the stuff about smooth muscle tissue growth is sound.
I'm pretty sure the tunica is always going to be the "limiting factor" for girth especially. But limiting factor might not be the best way to think of this function of the tunica. The tunica is what
defines the shape and size of the penis. Without it you wouldn't have a penis at all

It's called "tunica dispensability" in the medical journals. Increasing tunica dispensability for girth gains can be an elusive endeavor. I'm not sure it's possible for everyone.
As for length, unfolding or uncrimping ligaments or perhaps their point of insertion into the penile fascia, probably have some role in providing length gains.
These are just my thoughts on the matter. I haven't seen a theory yet that could explain the variability in gains reports. We just don't know for sure what's causing gains or who's making mistakes and who's lying

There's a lot of inconsistency in what guys are doing to produce their gains. But I know some of us have gained
something.
I believe everyone has a limit as to what they can gain. It's more of a potential in the tissue that is expressed and then gains are just going to stop. I could be wrong, but I don't have much else to go on.