Hi Ballroom and Steve, which oldie but goodie are you referring to? I don't see a link in your post Ballroom.
IAA are actually a UK auction house that holds auctions in Spain as well as the UK. Don't ask me why they hold auctions in Spain - perhaps some family or friends there.
The guy that runs IAA is Richard Davies. Like any authenticator he makes mistakes (e.g. he had to withdraw a traced Bruce Lee once - he did it immediately he got to hear about it being dubious on this site) but he is a long-time collector and certainly an expert in many areas.