The USAC website lost a lot of results this year sometime. Huge gap in results, mainly the mid-2000s to just about now. I have no more results listed early 2005 to mid 2017.
Discretion is key. Local administrator can make a judgement call. One racer came to me asking about starting category - he'd been on the Canadian National Team with Louis Garneau and Steve Bauer. They started him at Cat 3 (and it was appropriate). Another rider was a forever Cat 5 but a pro mountain biker. They upgraded him to 3 at some point, he was fine there, probably could have raced as a 2 but didn't place a lot as a 3 so couldn't upgrade. He was very strong though and could work hard all race long, I think he'd have been a solid addition to a Cat 2 race.
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"...during the Lance years, being fit became the No. 1 thing. Totally the only thing. It’s a big part of what we do, but fitness is not the only thing. There’s skills, there’s tactics … there’s all kinds of stuff..." Tim Johnson