I have seen similar occurrences and heard of many others. The leniency is ridiculous. I can understand some leniency here and there for very special cases, but like you said, it's more than norm than the exception. If you don't know the rules or just don't care, you have to pay the price for that. It makes me want to be an agent.
Good job! You have the timing of those whites dialed in! I'm always surprised they're doing their run this late by you. I suspect most WB runs on the larger tribs are done by now.
I'm saying it was a turtle from the description of chunks missing, but if it had any claw marks I'd switch my answer to otter. Especially if you were on the little Niangua. We have had a fair amount of issues with them. I second the notion of checking your line in the night. I feel like they bite the best before midnight, so a check around 11pm or midnight is the "sportsman" thing to do and then you can re-bait the line too and possibly double up!
I fish pretty far up around 85mm on the osage at least once at this time of year and typically catch one or two whites while we work the banks and docks for LMB's. I'd rather fish for whites and crappie, but I'm overruled. If someone catches one on a spinner bait, I'll cast back in with a white crank bait and rarely succeed with a 2nd white. We rarely catch a 2nd one on spinnerbaits either where we caught the 1st and haven't caught more than 3 out of one spot. I know whites and hybrids are supposed to be numerous way up the Osage, but haven't experienced it much myself.