just had a flick through the Dogs of War book- [...] curiously the Birdman of Catrazza were missing.
Some time back in 6th edition, the old DoW stuff from 5th edition (plus all the other mercenary units that had been released since then) was split into two lists, and later uploaded to the old GW website for free download:
1) Dogs of War. Mercenary army units from many parts of the Old World, but all of them generic units of their type (allowing players to use the various plastic regiments available for Warhammer and convert their army to their hearts' content). Most of the special characters ended up here, in particular the generals/lords/heroes.
2) Regiments of Renown. This is where all the named regiments ended up, and also any small duo/solo character units like Gotrek & Felix or Asarnil the Dragonlord. All of them can be hired into a DoW army, and many of them can also be recruited into most of the other regular WHFB armies (there's a matrix at the end which explains who will work for whom, and what army choice they count as in that army).
The list was updated a little around late 7th edition (I think...?) and remained "legal" in official games until the demise of 8th edition. The Warhammer Armies Project still keeps both books separate, and the Birdman of Catrazza are therefore in Regiments of Renown
here.