Quick question regarding "Legal to Start, Legal to Finish":

Yesterday I was assigned the below trip:

DEP ARR BLK
FLT 1 AAA - BBB 0900 - 1045 145
FLT 2 BBB - AAA 1200 - 1345 145
FLT 3 AAA - BBB 1500 - 1645 145
FLT 4 BBB - AAA 1800 - 1945 145

TOTAL BLOCK 700

This is what my schedule ended up being:

DEP ARR BLK
FLT 1 AAA - BBB 0900 - 1100 200
FLT 2 BBB - AAA 1200 - 1500 300
FLT 3 AAA - AAA 1530 - 1600 30 Return to Gate for MX
FLT 3 AAA - BBB 1630 - 1815 145
FLT 4 BBB - AAA 1930 - 2115 145

TOTAL BLOCK 900

I ended up refusing to fly the last leg because, in my understanding, legal to start legal to finish only applies when the schedule hasn't been modified. While I acknowledge that the RTG does not count as flight time in regard to scheduled limitations, I argued that at that point the schedule had been "modified" as a new city pairing had been added, and the pairing number went from "EX3000A" to "EX3000B".

So, what is defined as "start" in the legal to finish, legal to start conundrum? Is the schedule "restarted" after a return to gate or diversion?

I read the entirety of the ALPA "Guide to Flight Time Limitations and Rest Requirements" and couldn't find it.

http://cf.alpa.org/internet/projects...6-A_June04.pdf

Here's what FAR 121.471 (g) states:

A flight crewmember is not considered to be scheduled for flight time in excess of flight time limitations if the flights to which he is assigned are scheduled and normally terminate within the limitations, but due to circumstances beyond the control of the certificate holder (such as adverse weather conditions), are not at the time of departure expected to reach their destination within the scheduled time.


*Example and times adjusted for simplicity.