Building on (or instead of?) "seasonal curler comparison" and "...opposite comparison" it would be nice to have a report that lists all curlers who registered last season and/or this season. So each record would show Name, Primary email, User email, registered last season, registered this season. Thus in addition to showing who curled last season, and who has re-registered so far this season, it would show new curlers this season.

Perhaps as a quick interim, the Curlers tab could have two checkboxes, currently there is one for "registered this season", add "registered last season"?