The most important thing to remember is that upgrade explanations in the Rulebook are guidelines, not rules.  Think Jack Sparrow from Pirates of the Caribbean, not Moses with tablets from The Almighty.  Each request is evaluated on an individual basis and individual circumstances can be taken into consideration.  The next most important thing is to bear in mind that Greenbelt is a training race—the goal is for riders to actually get a race-like workout in the middle of the week, work on their skills and, perhaps, win a little prize.  In my opinion, Greenbelt is a tool to accomplish race goals, not an end to itself. - Tracy Rankin, MABRA Upgrade Coordinator

That all said, here’s my approach:
 
Experience upgrades:
5 to 4: Greenbelt is perfectly fine for gaining mass start experience and I generally consider them totally legit for these beginner to not-quite-beginner upgrades. Caveats are that you actually have to finish the events—you don’t need to be listed in the results as they are not usually captured for the entire field, but you shouldn’t be crashing out or DNFing for mechanicals for the majority of the events submitted. Just let me know in your resume how you finished: e.g., won, field finish, OTB, DNF mechanical, DNF crash
 
4 to 3: As part of the 25 mass start opus, I’m OK with Greenbelt B races as part of the resume. They shouldn’t be the majority, however, and you do need to finish with the field—not off the back. Of course, part of the issue is that you can, in the context of a training event, get dropped and then get back in to try and finish with the group and the entire group is not usually scored. But--see above re training nature of the event.

Points Upgrades
4 to 3: For points, this is where it gets a bit tricky. For a 3 upgrade, you should have accumulated 20 points. As Greenbelt would be considered a circuit race, you need to finish top 6 to earn any points—depending on the field size. Generally, the B race is a good representation of cat 4s, with some 5s, and the event meets distance guidelines and has a legitimate field size, but I usually don’t have a way to verify number starters and category of those starters on a regular basis. You should be beating mostly cat 4 riders, not mostly cat 5s. That said, a couple of Greenbelts for points is OK, assuming I can verify cat 4 starters, but solid top placings on the weekend are much, much better.
 
3 to 2: I would prefer that Greenbelt not be counted on for these upgrades. First, if you’re a 3 doing well in the A race at Greenbelt, then you should be killing it on the weekend and don’t need Greenbelt results for points. Second—the race distance is usually insufficient, given that it varies depending on the amount of daylight available and weather-related shortening. Same issues regarding verifying field size as the B race as the officials only have to score the top 5 for the series, even though they often capture more.
 
2 to 1: As I don’t handle these, I can’t speak to this class. But—I would imagine that winning at Greenbelt might not be the best venue for demonstrating national-level competitiveness. Unless it is the week before Air Force or whatever and all the big boys are in town. I’ll let Randy Inglis weigh in on this one.

The bottom line is if you are trying to move up beyond cat 4, you should prioritize doing well on Saturday and Sunday, not Wednesday.