Are people in the Secret Space Program put through a multi-year training and then regressed back to a young age more than once, and if so, what percent of recruits do double duty like this?

This is, in fact, in place and it is one of the ways they gain great hold and power over the humans involved. They can serve and be trained to a much, much, greater extent than is possible with conventional human military training. This solves the problem of the time span needed for greet learning and seasoning both, while maintaining viability through having the vigor of youth and not ending up with a highly trained middle-aged person who is becoming less robust and healthy because of aging. The way they can manipulate the mind with this process is such that prior training can be added at the outset with a second go-round. This accelerates the second tour of duty tremendously, much in the same way with servicemen repeating service through new tours of duty as they can be sent right to the front lines or to an area of intense military importance without great risk because of their training and seasoning. In the case of the Secret Space Program, training can be continued and renewed indefinitely, to keep the trainees sharp and to maximize their potential usefulness. And this makes good use of the time available while waiting for a final decision to implement these forces against humanity in a concerted effort on a large scale to proceed with annihilation.