I don't think the police were given information that Corrie might be in the landfill (therefore he could have got there some other way), I think it's about following a logic trail.
Corrie went into the horseshoe, wasn't seen coming out, never seen again. No one walking past saw him in there, and when the Look East reporter did his segment in the horseshoe it looked fairly well lit, so why didn't anyone see Corrie in there?
A) he went into a building -- no trace
B) he was hidden out of sight in a bin
We were told there was no forensic trace of Corrie in the bin, but we weren't told what kind of forensics were done on it. We were told the bin was too light to have contained Corrie when it was lifted.
But if you rule everything out and you're left with nothing, you've got to go back and start assuming at least one 'fact' is not a fact after all.
So I think that's what they did. Combine the fact that Corrie wasn't seen with the fact that the bin lorry was the first vehicle into (and out of) the horseshoe after Corrie was seen on camera, and assume the bin weight was wrong and that there's a logical reason that the forensics missed him being in the bin.
Then Corrie can be in the horseshoe for an hour and get out unseen.
Which, we are told, leads to the landfill.
Then they had the confirmation that the bin weight was wrong, supporting the decision to do the landfill search.
When you've got all those people walking past, the cameras, the details of the vehicles in that time frame.... I think you need to do the same again *if* Corrie is not found in the landfill. Limit yourself to just one or two tiny 'facts' being incorrect, not attempt to rewrite every fact, which goes back to the Occam's razor principle (the simplest explanation with the fewest assumptions is most likely correct) and Wella's comments about not making too many assumptions or excursions from the known 'facts'. The way I see it is like making paths through a flowchart, and we need to make as few changes to the 'facts' and as few assumptions as possible, and take into account that Corrie wasn't seen by a person or a camera after entering the horseshoe...Corrie hasn't used his phone, his bank account, presumably his NI number since that night. The police searches didn't find a body, the Sulsar searches didn't find a body. If Corrie lost his phone and it went alone to the landfill (to account for the pings) then why haven't the searchers found the phone in the landfill?
I think that's the kind of thinking process we need to be considering.