That was exactly my experience, only that the scar phimosis never went away for good. Some days, all would be supple, and some days, it would tighten like crazy.
During teenage years, I read urology books trying to find out if my long foreskin was normal. That is when I learned that partial circumcision was possible but highly recommended against due to chance of recurring phimosis.
After my first one, what I experienced was temporary, usually after sweaty exercises and easily reminied with stretching/warm shower and erection. Wrote it off not as a permanent thing but scar healing issue.
7 months later did anothers nip to get shorter skin and after leaving it retracted for a couple of weeks during healing, never experienced any tightness at all.
But I am guessing you were an example used by those who wrote those recommednatiosn against partial circs. But I think that once the skin is short enough (with scar not at meatus, but over wider part of glans) the problem doesn't happen.
I dount it was those anti-circer muscles, it was much more likely your scar which had tendency to shrink. But am susprised it woudl have lasted till you were 18. Would have though constant teenage masturbation would have widened the opening such that it wasn't a problem.
Perhaps in your case, the scar was getting "damaged" whenever you tried to retract foreksin, so lost much elasticity over the years.
Towards the end of my days after first snip, I had noticeed the scar ring remained wide at end of foreskin when soft. Indication that it wasn't very elastic. (but also reduced times when hard to retract). But didn,t likel the look.