My uncle is a conservation officer in Mississippi.I've known it to be enforced.Guy was caught poaching.(probable cause)CO's went to his home and found he was over his legal possession limit.Yes,it was in the freezer.
Guys who poach become known to conservation officers. If I was hunting deer, and selling it, sooner or later I would come to be known, and then you could bet I'd be challenged to the letter of the law. But I don't sell a deer a week, so anything I have in my freezer wouldn't be picked over.
I give away meat all the time, I don't bother to tag it. But, I should. You are right in that it is technicaly the law that it be tagged if it leaves my possesion.
The law however, isn't really intended for that, it's intended to catch pouchers.