The President shall have Power to fill up all Vacancies that may happen during the Recess of the Senate, by granting Commissions which shall expire at the End of their next Session.These appointments were not to fill a vacancy, they were newly created positions IIRC. The language is clear "that may happen" means there is a person in the position and suddenly leaves, dies, or otherwise can not perform their duties in that position, then the President can make an appointment to fill that sudden vacancy. I would argue past recess appointments as well if the position was open when the Senate was in session and the President waited to fill it during a recess.
That is the subject of a separate case, I believe in the Third Circuit IIRC, which interpreted the recess clause as you have stated. No recess appointments unless the vacancy occurs while the Senate is in recess.
I wish I had more confidence in the Supreme Court. Just tell John Roberts a lie and he’ll buy it. And this regime excels at lying.