Going back to Stafford, 9 of the last 11 #1OA QBs were the starter in week 1. Only Goff (starter by week 10) and Mayfield (starter by week 3) weren't.
For top 5 guys starting with Stafford, 17 of the 23 were week 1 starters. The two above plus Bortles, Trubisky, Tua, and Trey Lance weren't, but...