The topic of mandatory harvest reporting has come up frequently in the past and is something that I personally support. A few years ago I broached the topic with CPW staff who are responsible for surveying CO hunters and compiling the data and they cited the cost associated with a mandatory harvest reporting system and referenced the paper below. I misplaced the paper at the time and couldn't remember the title, but I located it yesterday when working on my decennial office cleaning and found a web link. I'm just sharing for your edification.
Evaluating Cost-Efficiency and Accuracy of Hunter Harvest Survey Designs
Evaluating Cost-Efficiency and Accuracy of Hunter Harvest Survey Designs