Agreed with all of that--BUT, the scenario the OP raised was having a stand-alone RES ("on call") day at the end of a month. None of those reasons (possible exception of child care) could be played in this scenario--your [his] schedule had RES on the last day of the month from the get-go. Even the child care card could, I imagine, land one in hot water ("Well, Mr Driver, you were scheduled for a RES day, and the PWA clearly states you could be flown into your REG month--why didn't you have child care arrangements for the day(s) in question...??").

As I read it, that laundry list of how assignments aren't absolute ("proffer or not") essentially applies to a trip assigned to you at the last minute, starting on a day when you didn't expect to be flying / on-call.