My understanding is that there's a difference between being Explorer and any other status above that.
So... Explorer will get reset to 0 every year if they don't reach 100XP. But someone with status from Silver+, do have rollover.
For example: as a Silver member, if I had 120 XP at the end of the qualification period, 100XP would be deducted to keep Silver, and 20 would rollover to the next qualification period.