A recurrence rule is added to a start event, then an occurrence cache is either generated on the fly for periods of interest, or, yes, a rolling cache a year or two in the future is maintained and updated daily.
Perhaps trivial, but actually seems like an interesting question given you have to potentially tradeoff RPCs for routine queries (and the number of database records) vs. being wrong for the random "Am I free on this day three years from now?" query. Of course, the answer may be that, in general, the differences don't really matter.
