[Stooky Bill]

Did the Thames name ever truly disappear though? I do remember the late 1990s logo with “Thames - A Pearson Television Company” with the once proud logo reduced to just Tower Bridge, but was there any period when it was just Pearson TV, with no sign of Thames? If there was I think it may have been very brief.

No, it never disappeared entirely, but Pearson did use several brand names in the late 90s/early 00s (Grundy and Fremantle most notably) and they did seem to start getting more prominent at the expense of Thames before the end, then in 2001 they got rid of the other names, in the UK at least, and used the Thames name exclusively.

Pearson were the first production company (I think) to split their productions brands into genres, which is fairly common now. 

So if their programme was a game show it became a Grundy Production, if it was drama it was Thames - both The Bill and Family Affairs were Thames, and IIRC Alamo was comedy. There were a few exceptions, for example Neighbours sensibly stayed a Grundy production, not Thames, and This is Your Life stayed Thames

This changed towards the end of Pearson ownership when they bought Talkback and merged that with Thames to become Talk back Thames. This was the nearest the Thames brand came to disappearing. 

In 2011 the new owners RTL/Freemantle split Talkback and Thames and did the genre thing again with Boundless for factual shows.
Retort for scripted comedy. Talkback for comedy entertainment.Thames for entertainment shows.... hence X Factor was a Thames show