There is no way to set a time frame limit on counting the program success. You could remove the person from the old program if you really wanted to, but not a great scalable way to manage this. I'd submit this as an Idea if I were you - I have thought about this before as well.
That being said, I haven't considered this multiple opportunities being closed-won before. I have always assumed that once an opp is closed-won, the multi-touch "resets" if you will.
Well, it's rare that you would run a PM or PO report that would look back 3 or 4 years, so I very much doubt you will encounter this problem. When I did this by hand, my rule was a 9 month window from the touch. Your company may want a different window.
In the reports, you will only say something like "Show me Opps (MT) with touches in past 1 year." or Opps Created in X window of time.