Someone forgets that it is Rosh Chodesh and davens a regular shacharis. He does not remember until zman mincha. Before he does anything else, he has to daven mincha with Yaaleh V’Yavo. Does he also have to daven tashlumei shacharis, or does it have the same din as someone who forgot Yaaleh V’Yavo in shacharis and only remembered after mussaf?
It has the same din as when he remembered only after davening mussaf. The reason is because those poskim who say that davening mussaf is like mentioning Ya’aleh V’yavo, it was already mentioned even though now it is the time to daven mincha.