Note that the qualifying rules for the U.S. Championships have varied greatly over the history of the event. The regional qualifying event structure was not uniformly put in place until the 1966–67 season. Also, prior to this time, at sectional qualifying events skaters competed at one level above their national level, so (for instance) senior sectional champions qualified to skate at the junior, rather than senior, national level. Qualification for the senior national championship was through a separate set of rules, essentially based on results from the previous season. There have also been changes at various times to the number of skaters qualifying through sectionals, and to policies for byes.