This is a good point, I suppose a guy who caught the fish maybe thought he needed physical evidence to collect the money, but didn't want to keep the fish. I've only caught one tagged fish that I know of, and released it with the tag still on. My brother and I were fishing and he brought a video camera with him. You can see the tag in the video but I released it without even knowing it was tagged, Duh.
Anyway, those tags are pretty darn small, can you actually read the writing on them?