I believe one of the non-Boston specific shirts had a couple sizes sold out but other than that everything was in stock. They said they had stock saved for the other days so just because something sold out today doesn’t mean it’s completely sold out.
My Noah kahan Fenway merch experience for anyone wondering: I got there at 5:15 and got to the front of the line at 8. At around 6:30/7 they ran out of the Boston pennant and at 8 the ran out of the Red Sox hat.