It makes one wonder if the couple supposedly seen outside 37SR were a clever piece of misdirection.
There are no reported signs of SJL having been inside, eg fingerprints. She could not have avoided leaving fingerprints inside if she really had conducted a viewing. They would be on door handles, light switches, banister rails, worktops, and so on. If there were loads but we just don't know about it, certainly the CPS at least would have been told. The CPS, however, have said there is no evidence linking SJL to JC. They wouldn't have said this if there were her and his fingerprints inside 37SR. I infer there are not and hence neither of them was ever there.
So the hunt should have ignored 37SR from the outset, because it's clear by deduction that she was never there. But if you sent a couple of accomplices to turn up and get noticed there, you may persuade a suggestible investigations team that she really did go there. If you do that, and they release that assertion into the public domain, that becomes the narrative - and it still is to this day. Meanwhile, nobody who saw anything weird happening several miles away is going to speak up because they've already been told where she last was and it's not in (eg) Acton or Chelsea.
OK it's a bit of a conspiracy theory, but for someone to disappear essentially without trace, there really does seem to have been some sort of conspiracy.