I'm quite certain Scotland yard will have read the files, and haven't dismissed the Smith sightings so readily.
I think the mistake is to suppose that what we read on line is word-for-word the same (as the files held by the McCanns and the police).
Perchance they are thinking, as I am thinking, that Tannerman stopped off en route, quite possibly at the Staff Quarters just a few metres up the road from the forward Smith, (was it Peter?). Madeleine was very cold and a cardy, or cotton long sleeved top, was found to keep their precious, money making little one warm.
To remind you, A scream was heard coming from the Staff quarters according to the 3 A's
I originally thought that Tannerman might have stopped off there because he had been abandoned by his get-away driver and had nowhere to go, but there is another possibility.
Maybe he was to go there to send out a signal to sea thta the mission, part 1 was completed ....and await a return signal from a boat at sea that a "pick-up" boat was coming in. ... and he was to leave to "connect" with that boat?
This may be completely incorrect but the staff quarters are high and I would have thought from the roof there would have been good visability of the ocean.
This is just an alternative idea to my original one, both are possibilities.
And once again, to remind you, it seems that
A scream was heard coming from the Staff Quarters