Might be a silly question in hindsight but I presume Channel 4 as routed through the ITV companies only had the one region for each area, ie they just had "Midlands" as opposed to separate ones for Central West and Central East? So Channel 4 viewers who saw Central News East would see adverts having been inserted at Birmingham, not that it would have really been that noticeable?
Yes. But the C4/ITV subscription era pre-dates what we now call sub-regions.
The regional splits in ITV were the dual regions Central into East and West (as you pointed out, Nottingham was up and running) and TVS Southampton and Maidstone. Did Central actually play its ad spots out from Nottingham?
TSW had its news splits, which came out of its own franchise commitment rather than being an IBA mandated dual (errr quadruple) region. TSW was one region for ad insertions. I believe that I'm right in saying that you couldn't buy bits of the region separately. Belmont had its 7 minutes of Calendar, but did Yorkshire ever sell Belmont separately in the 1980s?
All this pre-dates the halcyon days of sub-regionally with Meridian's five separate tx groups (Rowridge, Heathfield, Hannington, Midhirst and BBH/Dover) ; Anglia's Tacolneston, Sudbury, Sandy Heath. ; or Central's Abingdon.