To be fair, he did have heavier periods where he ran the weight up bit, trying a max (#500 lb bench, etc....), here and there. He just had smart rules he didn't break as he got older, for instance, he almost never dropped below 5 reps for the majority of his training, he swapped things out if they got painful, etc....
Here's a nice vid he did as an older man looking back on his training, etc.... -
.
He was also calf checker, if a guy didn't have good calves, and couldn't figure out how to improve them, then that guy was going to have a hard time in bodybuilding.