Apparently PBS doesn't have some kind of massive conglomerate backup or archives of things that its member stations produce. It's up to every station to archive or back up their own stuff. No standardization as to storage formats, NASes, tapes, or anything.

Sometimes things are transmitted in painful ways like rebroadcast in off hours over microwave links between members so they can re-record what they lost.

Plus the endless game of "hey does anyone have that one obscure episode of this one program we made?" to your colleagues...

It's the original torrent network