To make a long story short... Paul D was right, I was wrong.
Mea culpa, mea maxima culpa
We were all in agreement on this much. Once a player is added to the 40 man roster (which must happen in his fourth year as a pro, otherwise he is exposed in the Rule 5 draft), he has three "option years." During these three years, he can be optioned to a minor league team. As often as the major league team feels like, it's entirely a matter of the team's discretion.
What we seemed to keep going back and forth on was whether the option years ticked by, one after the other, once a player had been added to the 40 man roster. In which case, John Olerud's three option years would have been 1990, 1991, and 1992. Or whether an option year was used up only if the player was actually optioned to the minor leagues. In which case, John Olerud still has all three of his option years left, which is surely of interest to someone.
I have been in touch with a Higher Authority, a definitive and reliable oracle... and John Olerud still has all of his option years remaining.
Oops. My bad.
In a somewhat related subject, if a player refuses a minor league assignment and chooses to become a free agent, his team is no longer responsible for his contract. He's on his own.
The team would be responsible if they gave a player with a guaranteed contract his unconditional release. Said player could then sign with any other club for any amount whatsoever (it will always be the minimum) and his original team would have to make up the difference (see Doyle Alexander being paid by the Yankees to pitch for the Blue Jays in 1983.)