Marty - I'm involved in a couple volunteer fish tagging programs and asked same question.
Most times - no matter the species - a 3-5 % return is expected.
There are some variables that come into play.
#1 - Tag has to be legible for return. Some tags wear away after a long time. I've seen Tautog tagged off OC be nipped at by other Tog. They nip away much of the tag.
#2 - Whom ever recaptures it - must turn in the tag or call it in. The shark tags I use have instructions printed in about 7 different languages. Imagine a tagged shark caught far away by some one without education.
#3 - Whom ever recaptures the fish must be willing to call it in. Some commercial fisheries will not return tags - in fear recapture info could lead to less quotas.
I think there were more then 11 Diamond Jim tagged Rock caught. Heard 4-5 were disqualified
.
I've caught a few tagged Rockfish - most were at large for over 18 months.
I think a few years ago - a Diamond Jim Rock was caught in January at CBBT.