[James2001]

It must be. If it was the 1989 corporate one it couldn't have the copyright year on it.

Some ITV corporate endcaps have the copyright year on- the second series of Wheel of Fortune, which has been shown quite extensively on Challenge, does for a start, as do many of the 1989/90 episodes of Take The High Road currently on the STV player, so it's something STV did at least (interstingly, on the first few weeks after the corporate look came in, the jingle from the previous endcap plays under it- so clearly the new endcap corporate was edited onto a bunch of episodes at the last minute). I'm sure I've seen a Tyne Tees example too.

Edit, yep, looking at TV Ark on the Wayback machine, there's Tyne Tees examples from 1990, 91 and 92 (so presumably there's 1989 examples out there too, so it's quite possible the Supergran version was corporate):

web.archive.org