if you flew the legs as scheduled it pays the rotation guarantee, even though underflown. for example, last month i flew a Gs originally worth 22:38. We over blocked a few legs and were up to 23:21 mid rotation...but they ended up chopping the penalty lap off at the end of the rotation on a reroute and we finished early...the trip dropped back down to 21:03. So i got 22:38 orig guarantee + 21:03 as flown.