I think losing all your cemented gains is to all extent and purposes impossible. Substantial amounts, now that’s another question. Thunder said he lost very little, same with Bigger and both haven’t PE’ed for some years.
Personally I stopped PE in April 2003 and have done 1 month of ADS and maybe 2 weeks - 1 month (maybe a little more but not much) aperiodic jelqing since then and I lost a little girth (hard to quantify but under 1/16”) and maybe as much as 1/32” real length and a little more from less hard erections, though again there is an error factor there.
What you might be thinking of is this thread from Dino talking about JAPP’s losses. As JAPP is an active member here, he can no doubt add more if he wishes but he’s already talked about this here I think. He talked about loosing 50% of his gains in 2 years.
There’s also been one other guy I remember mentioning losing a bit, but I can’t remember who right now.
Losing gains incredibly quickly, within a matter of weeks is impossible.
I think in all likelihood that gains from stretching the tunica are extremely hard to lose but maybe the ligs tighten a little and the erection level lowers a little and this is responsible for a fair amount of what people count as losses.