Stuff like that happens all the time. Often the "masters" of early TV programs were discarded shortly after initial airings as few people saw their future worth. I've read in several sources (wish I could remember just where though) that this is what happened with many early productions. They were disposable entertainment and once aired, they disposed of them. Even if a major participant had the foresight to hang onto a copy for posterity, family members don't necessarily share that vision and enthusiasm and get rid of the materials. For example: I'm no producer of entertainment but do have several collections, some of which have value in the collector's market, that I absolutely know my wife would simply dump in the trash should I beat her to the grave. She's said this on several occasions, in spite of me having a list to make things easier. She doesn't want to bother with proper disposal. Fortunately my kids and grandkids know of these and would intervene but they'd have to hurry to beat her to it. I'd imagine there are lots of families with identical issues and that's what happens to lots of "missing" material.