Marriage "contract date of July 24, 1423"
— https://www.wikitree.com/wiki/Forbes-144
— https://www.thepeerage.com/p41377.htm#i413768
ONE OF THREE POSSIBLE OPTIONS ARISE PER THE CONTRACT DATE:
OPTIONS A: William Forbes, Thane of Kinaldy, 1st of Pitsligo and Agnes Fraser and had no children, which may mean the mistress(es) bore them all.
OPTION B: The marriage contract date is be wrong. If so, what should it be or not be per a source?
OPTION C: The children's estimated birth years, then, begins c.1423 and later.