The thing about Tannerman/Crechman is that their appearance and clothing matched rather well. Add to that the fact that they carried a small child which was also similarly clad, introduce the timng and the chances that Crechman was Tannerman is not absolute but very compelling. I don't think Redwood would have stuck his neck out on live national TV if he wasn't reasonably convinced. What worries me about this though is why Crechman never came forward to clear this up years ago and why even now he was gven anonymity when others in Portugal haven't?
One article (posted on here ages ago) stated that he did go the police back in 2007 - but it didn't state which police. If he did, then his statement may have been overlooked until the review.
I never got the impression that Redwood had formally eliminated Tannerman, but believed that there was a strong possibility that Crècheman was Tannerman. The point being, IMO, was to give more emphasis to Smithman to try to jog memories of that later timeframe.