They haven’t updated all in one go since the ’97 rebrand… the early ’00s rebrand was staggered from 2001-3 (’01 BBC Two, ’02 BBC One and Four, ’03 BBC Three) , and the late ‘00s rebrand was staggered from 2005-08 (’05 BBC Four, ’06 BBC One, ’07 BBC Two, ’08 BBC Three)
Well even 1997 only saw a tweaking of BBC2 idents to incorporate the new logo. Agree though that an all in one revamp is what the BBC needed really - BBC2 was revitalised overnight with it's revamp and if that could have been achieved across all televisiual outlets at least it would have revitalised the BBC as a whole.
C4 haven't really updated everything at once, though ITV of course did back in 2013 (and again in 2006, though I think then ITV4 went to air with the new logo earlier when it launched)
Shouldn't that have been posted in the "John Logie Baird has Invented Television"