As said, call the contract hotline. These provisions changed for LUS recently so you won't find a lot of "institutional knowledge". I read it as you do... You don't get paid for cancellations before you report for duty, unless it's the last trip of the month.
Similar question on my part, two back to back 2 days, end of the month. The first one gets extended to a 3 day and kicks me out of the second 2 day. Do I get paid the original value of both trips? Just the 3 day? The 3 day plus the 2 day (double dipping)? My interpretation is I'm protected for the original value of the 2, 2 day trips (or what's flown, whichever is greater).