Anglia & Meridian 1999/2000

The only example of the [itv] logo being added to the Anglia flag ident online was a screenshot on the now defunct TV50.org.uk website...

Anglia page from TV-50 on the WayBack Machine

Unlike the Meridian example, here "888" now reads "Subtitles" if that helps date it.

Given Meridian and Anglia did this, it would make sense that HTV would also add an [itv] logo to their ident. But I don't recall ever seeing an example of that!

No, never seen that, and to my knowledge, that never happened. Also, not sure of the exact date, but presumably as HTV West TX only moved over from Cardiff to Southampton in 1999 IIRC, that probably had something to do with it in terms of timing.