Mostly correct. When you join the military initially, you incurr an eight-year mandatory service obligation. If you seperated after your initial enlistment, you can still be recalled until those eight years are up (you'll be moved to the IRR if you don't join a reserve unit after you leave active duty).

However, once the MSO is up, then the only ones that can be involuntarily recalled are retirees.

Good question. I believe you are correct but don’t put a big wager on my guess