But it is not at all remarkable that these old episodes still exist somewhere (after all, the original films are probably still sitting in their studio vaults). Of course, it is a marvel of modern technology that those episodes are now accessible to the general public - even only on a whim (and even if illegally).
But what is remarkable about your personal experience is that, when re-watching an episode for the first time after 45 years, you could recall every individual camera shot. The human mind is more amazing than Youtube.
And about the Political Correctness rampant today, and how HH could have been filmed in the 1960s/70s: It is because the WWII vets had just reached their prime that there was such a potential demand for such shows. And it was because the show was so unrealistic that no one felt offended.
Incidentally, another show, "Campo 44," about Allied POWs in an Italian camp, preceded HH.
Regards,
According to IMDB, Campo 44 was a pilot for a series that was shown as a TV movie in 1967. Hogan’s Heroes was a series that debuted on TV in 1965.
https://www.imdb.com/title/tt0143163/?ref_=fn_al_tt_1
According to TCM, it was an attempt by NBC to copy HH, which was on CBS, not the other way around.
http://www.tcm.com/tcmdb/title/462077/Campo-44/