Here is the reference:
i. The value of a given bid period’s deviation bank shall be equal to the value of:
(a) the applicable fare(s) for the scheduled commercial deadhead ticket(s) for all trips flown during that bid period; and
(b) the value of the applicable fare(s) for the scheduled commercial deadhead ticket(s) for recurrent training scheduled during that bid period (if any).
If you fulfill your sub, you are considered to have flown the trip. If you decline sub, you haven't flown the trip. I have had this happen to me.