I doubt there is any kind of "proof" that would satisfy the unbelievers. There's far too many variables involved in order to quantify successes or failures with odor reduction practices.
It's pretty much anecdotal, which can actually be relied upon when put into relative context.
I can only speak for myself and what I've experienced over 50 seasons and a evolving process of odor reduction. I've done pretty much everything except for going strictly vegetarian...not sure I could do that.
I can say with absolute certainty that as my odor reduction got more extensive, my odor busts got less frequent and less intense. My wind reading skills and understanding of surface behavior has also improved dramatically which has been helpful towards determining how well my odor regimen has worked. I say it a lot...I just don't believe that there are very many hunters out there that truly understand surface wind patterns. If a guy doesn't know what the wind is actually doing, then it's hard for that guy to really know how well his odor regimen is working. And I'll venture to say that just as many hunters are not very skilled at reading the body language of deer. Lots of hunters believe that they were not odor busted when in reality the deer did bust them to some degree. The question is, to what degree was the bust? I am firmly of the belief that we cannot become totally odorless but I also firmly believe, with diligent odor practices, we can reduce the frequency and severity of the busts.
There's no doubt in my mind that my hunting is far more enjoyable when I experience a non, or minimal bust than the days before my regimen. I've done this long enough to have all the proof I need to realize this is "working" (I prefer the term "helping") for me. It's not 100%, nothing is.
I can't cite a mathematical formula, or a scientific study that proves my point. It's strictly from 50 seasons of observation.