I thought everything was in Leeds? bar local news stuff which is kept at the news rooms?
As discussed before a lot of regional news archive has been taken in by regional film archives, notably the south west and midlands.
I would have thought that Leeds would have some regional news archive, you wouldn't expect one of their regional news centres to hold 60 years worth of news archive (and the same goes for the BBC)
And of course the ITV Archive won't have all of ITV's archive, none of Thames, Southern, Redifusion, TVam and STV/Grampian.... and the One we don't mention
Although on the other hand it probably contains some non-ITV material, such as the films that Carlton owned