When the NCAA changed the rules that allowed incoming student-athlete freshmen to take summer classes before their first fall semester it changed the whole situation. Now an incoming freshman can have say 6 credits under their belt before the fall as well as working out with the S&C coaches before fall practice.
Also now about 99% (if not all) are on campus all summer long taking classes. Basketball has been doing this for a while now because basketball players take only about 12 credits both fall and spring because of travel.
Football (an estimate) now takes a course load like this:
Freshman Summer 6 credits
Fr Fall 12 credits
Fr Spring 15
First year 33 total
Soph Summer 6-9
Soph Fall 12
Soph Spring 15
Second year 33-36 (total 66-69)
Jr Summer 6-9
Jr Fall 12
Jr Spring 15
Third year 33-36 (Total 99-105)
Sr summer (6-9)
Sr Fall 12. (117-120)
Then if necessary finish up in Spring.
So of course this aggressive, and there will be some players that will take 15 credits in the fall during the season. I doubt that they would limit to only 12, if they think that they can handle 15.
Maybe the majority of them take 15 in the fall and then drop to 12 if necessary. So you can see how they can finish early.
Disclaimer my math may not be 100% correct as I’m trying to finish in a hurry.
Your numbers are good, and illustrate how it is nearly impossible (at least very ambitious) that any kid would be expected to graduate - with a meaningful degree - any earlier than his "4th year of playing football", ie the "3 1/2 year plan" that CJF often refers to.
CJF uses that analogy - or plan, if you will - to illustrate the ability to leave for the NFL after one's 4th fall semester (and spend the requisite time over the winter/spring at the NFL combines and workouts and what not), with a degree in hand.
It is a do-able plan for a kid who is disciplined (and doesn't start out behind - and have to take a first year of remedial classes), but it does require that 4th fall semester.