My own personnal opinion, stepping away from the too technical, is that if the weld deposit is solidified by the time the trailer arrives then the heat inputs should be considered seperate. This, in my opinion is code compliant, since the code doesn't really address it anyway, and generally metallurgically sound.
Heat input as well as Charpies, are an approximation, good ones to be sure, in my opinion, anyway, so there seems to me at least for now, little point in gettin too picky about exactly when to add em or seperate em. The solidification point is a good as any I suppose.
I would certainly welcome disagreement here. This is a good discussion.