I believe that he is correct in the sense that the stretching of ligaments tends to be more temporary in nature than altering the tunica. Ligaments tend to tighten and/or retract as we age. I myself lost an inch from my teens to my mid to late 30’s and I believe ligs were much a part of that loss.
I believe that if all of your length is gained from ligament stretches alone and no tunica work is done after you have tapped the ligaments to their max ie; 11 LOT down to a 6 LOT, being indicative of maximum gains in ligs per LOT theory (which I happen to agree with) then you stand to lose atleast some gains over time without maintenance stretching.
Tunica work, I believe, is a much more permanent gain. Not to mention, girth increases will also be limited if you aren’t working that shaft like you stole it. I have never personally gained length from jelqing. I have gained good girth, but everyone is different and is affected differently from these methods. They say that jelqing at low levels like 25% erect will gain you length. That makes sense, because if your jelqing at 25%, brother you’re stretching that weiner! Just my .02