[MFTJA]

Admittedly, it's not just the BBC, I know in Supermarket terms, both Sainbury's and Somerfield had lengthy periods using 2 different logos at the same time, and so did Comet.

Walking around my "local" Sainsbury's (which admittedly I don't do very often) the previous two logos are still very visible in different sections. 

One of the biggest companies in the world, Apple has been guilty of slow rollout too. Their previous glossy logo mostly stopped being used shorty after Steve Jobs passed, but wasn't completely gone until 2016 - about 4 years later