Baby Back ques

Sounds as though they might have been undercooked. 80 lbs of ribs means you're going to get variances in weight, fat striation, etc. I'd recommend spritzing with apple juice once @ hr and probing the meat between the bones with a toothpick, checking for tenderness. That's a lotta racks to probe but you'll get a better sense of when the meat's done.

I'm certain of two things.

One, no two ribs cook alike. You cook that many, you'll have some variance. The key is looking at each rack and knowing if it's done or if it needs more cooking.

Two, no two ribs come from the same pig (will statistically anyway) so you'll have some difference in the rib itself.

Maybe they were overcooked and dry, maybe they didn't have much fat, hard to say.