Nothing more was asked in those years -- he just started more games. I can't say I followed his career closely at all as I was a kid when he was in the NFL. So I don't even know why he only played in 16 games twice in his career -- he missed games almost every year. Maybe he was injury prone?
That being said my degrees dealt with numbers (accounting undergrad/minor in mathematics, finance postgrad) -- statistics is one thing I am very capable of discussing.
You can't cherry pick a set of numbers and say -- see he threw more int's, unless you have a subset that states those interceptions occurred once he passed his career median per game.
It is why you take the numbers from his career as a whole why, no matter how many attempts you add, if it follows his career averages, it will always come out as more TD's than Int's.
Now if you go to the game logs of each season you stated and it said after he reaches his career average of attempts per game -- his interception rate increases -- then it'd be a viable discussion point.
In the end -- it isn't going to change my thoughts though. Very few QB's during his era achieved what he did in college and the pro's. Was he a superstar? No. The guy was a journeyman QB, but he was good enough to play 14 years and to be the starting QB for 4 different teams.