What would be the reason for all the studios and pres areas having their own independent SPGs?
It sounds as if that would cause far more problems than it would solve?
Presumably because the ITV network was reconfigured several times a day. Before synchronizers the pres area had to sync with the incoming programme during the link which preceded it. (Hence why much of the presentation elements came from cameras, slide scanners etc which didn't object to adding or losing a few lines whilst on air rather than VT
which most certainly did). Being able to do that without affecting every edit suite in the building had advantages.
Presumably studios had the same to facilitate locking to outside sources.
At the BBC it was the other way round, the incoming source had to adjust its syncs to match NC1/2. Some of the bigger regional centres had two pulse chains, one that was fixed and one that could change without notice. So edit suites would be on one chain and the studio on the other, which presumably meant that having to genlock the studio to contribute into Nationwide and then re genlock in other to opt out was less of a headache for any late edits.
Write that down in your copybook now.