That's not the whole of it, though, because many of those recycled actors played characters with little or no prosthetics. This was going on since the original series and plenty of other shows before that, as well as shows today. (The various "Law & Order" shows do this a LOT! The "CSI" shows do it too. So did "NYPD Blue".)
Right, it's a longstanding practice. In recent years I've been Netflixing old shows like Mission: Impossible
and The Rockford Files
, and it's interesting to see how many times the same actors show up in different roles, sometimes not that far apart (though rarely more than once per season). I think the most frequent Rockford
guest who played a different character each time is probably Ken Swofford, though Gerald McRaney comes close.