..........and when I talked to the vets at UCD (while one of my snakes was undergoing a biopsy), two of them (including one with over 25 years practice) stated they had never seen it.

So c'mon - is this something you have experienced and verified with a biopsy?
Yeah, actually I have. I lost a number of baby corn snakes 15 or so years ago when I was keeping them on sand. Upon their deaths, they were necropsied and were found to be packed with sand.

Most vets are dog and cat Dr's and few of them even have any experience with reptiles and those that do generally haven't seen many cases so it's not surprising that they haven't seen it. But yes, it does happen.