Not sure, but I guess they may have realised that when they introduced the clean feed for the nations they could route the same feed to TC9 and allow them to join programmes via transitions and credit squeezes before NC1/2 took the programme directly.
That might have been after they left TV Centre. I don't think the suites there had the facility to do an output with the programmes clean. IIRC they had to select the correct source.
There was a time (I wish I'd recorded it now) where the presenters interviewed some celebrity, and the intro was playing on the screens like the credits are here.
But it took so long, they never actually managed to introduce the show in the time the intro had. However the episode didn't follow, the intro just looped again (straight away, it's not like it rewound on air) and then the presenters apologised and introduced the show and then it switched to full screen.
This was around 2004/2005 ish. So I'm wondering if the CBBC gallery had individual versions of the intros/credits and pres played out the episodes, or whatever was on these screens was the 'nations and CBBC feed', and someone in pres was quick thinking and replayed the intro.