Without going all geeky on this, when I did mine the second time, I did some research into ACL injuries and I read that there were studies done on rugby league players with knee troubles when they’d retired.
Turned out some had torn or even ruptured them and never known, they just carried on playing (for years in some cases) never having an ACL injury diagnosed but the muscles around the knee stabilised the knee, effectively doing the job of the ACL.
It was only when they retired, got older and had muscle wastage that they found that the source of their pain and instability was due to things like ACL’s being torn during their career. In some cases the ACL being absorbed completely.