I think you've nailed it above. Also, your VI comment is right on if he's a product of a college ROTC program. If my memory serves correctly, ROTC officers don't have a chance to switch to RA (Regular Army) until their promotion to major....he's still a captain. Therefore, his commissioned obligation is under a VI (voluntary indefinite.)
He would have incurred additional civilian school training at some university and he would owe a minimum of 3 years for that opportunity.
This changes my analysis somewhat. First, no captain with 17 years active duty could possibly have been commissioned that entire time. My guess is that he had enlisted time, got out and went to college during which time he obtained a reserve commission....perhaps some kind of green to gold or "bootstrap" program to move enlisted up to commissioned rank.
Had he begun as an officer and failed to make promotion to major at about the 9-10 year mark he would have been released from service. That's why I say he spent his time as an enlisted MP.
After college he probably got cute and didn't want to pay back the obligation but wanted instead to go to a cushy civilian job. The rest of the analysis still holds. I missed the 17 year statement in a quick first read.