[Stooky Bill]

Of course, in those days, BBC One HD network always had the red screen in England; regional variations also were produced differently as the signal physically when to the region (carrying network feed) and back to coding and mux (so was always sent “through the region” in a way that it isn’t now - with opting in and out physically happening at the region site). As part of the preparation for the HD regions upgrade, play out was changed so that regional opting is now controlled by a “switch” in playout instead, but regions can remotely control the switch - allowing them to maintain some autonomy if an emergency opt is needed. So there is no longer a need for the feed to go via the region and back again before coding and mux.

Tbats not quite correct. The opts take place at coding and mux. Each region presses a button to put themselves to air as they always have but that takes place elsewhere. 

BBC1 does still go through the region however as its needed either side of the opt outs so the galleries can cleanly opt in/out. That's why, in regions with only SD facilities the picture quality of BBC1 HD for a bit before and after each regional item - they're taking BBC1 through their SD gallery. The network feed is down converted going into their router.

Incidently coding and mux also took over the adding of any channel logo bugs (or DOGS if you must). They're all added downstream of playout but triggered by them. I'm not sure but I think the BBC1 SD overlays are being added in the same way.