One thing rather interesting to note is that the majority of these missing episodes were from the show's first three seasons, produced between 1969-1972, which would account for over 400 episodes, so that's about 7.1% of those over 400 episodes missing. Perhaps these were the unlucky ones to be victimized of being wiped, as was common at most television networks during that time. I think by the early '70s, that practice slowly started to die down (at least for scripted programming), as the cost of tape became less expensive. It's worth noting that The Tonight Show Starring Johnny Carson ended the practice of wiping their tapes by May 1, 1972. As for the three additional episodes from after those first three seasons, heck if I know.