[DTV]

It's the advantage they have of changing the logo to one that's not really that different to the old one. They can get away with having the old one present more than they could if it was a more radical change

But then this is just further evidence in the 'this rebrand was totally unnecessary' column. Indeed, the original plans for the Reith rollout specifically involved retaining the 1997 logo due to the unnecessary costs in replacing a logo that was fine as is. The decision for the newer logo was impulsively taken rather late in the process - which in itself is rather indicative about a lot of this rebrand.

But the custom curved glass will clearly take a lot longer to replace than, say, the more traditional signage on Television Centre when the logo was updated with the then-new Gill Sans blocks in 1998.

I don't see why it would take longer. If things were properly organised, the sign would have been made ahead of the changeover date and then it's merely a matter of changing three panels. The 1997 logo installation would've been far harder - affixing 19 separate signs to a brick wall and ensuring they're all aligned correctly at a far greater height - much more challenging. Plus, my assumption about the NBH logo has always been that its merely adhesive frosting - maybe I've not been close enough, but it doesn't look to be part of the glass itself.

And, as Michael says, the Television Centre logo was changed pretty much as soon as possible - you can see the new logo (Television Centre wording and all) in episode six of I'm Alan Partridge, which was transmitted 08/12/1997. I think it's safe to assume there was a turnaround of a week or two - so the logo must have been installed by at least late-November, if not earlier.