I've seen a few posts questioning how the mistake could be made. I've got a little experience in a similar(ish) industry. For a few years up to a decade ago I worked as a developer for a distribution firm - we distributed and collected goods from retail customers. As part of my last project there I wrote software interfacing with the companies weighbridges at their depots. When a van left the depot the driver would enter his ID and the ID of the "round" (the set of retailers he was delivering to) on a keypad and drive over the weighbridge. Being antique by 2007 standards this would be wired up by RS485 to a dot matrix printer. The printouts would then be archived (my mini-project was to parse the output and load it into a database instead). The printouts themselves were quite opaque, full of various figures and acronyms as well as the ID's the driver entered, and were fun to track down if an accident occurred and we needed to know
Now I'm sure that Biffa's IT isn't cottage industry like that, but it gives an insight into how mistakes could happen. We know that the fact the customer wasn't charged by weight was a causal factor in the error occurring. What that suggests to me is that if they were, the driver would have keyed the weight into some kind of track and trace system, perhaps after scanning a barcode or something on the bin. But in the absence of that data, they maybe needed to look at the raw output from the weighing device, which may have been more difficult to interpret.
I can see several possible causes of error:
* A simple misunderstanding of scale (e.g. 11.2kg instead of 112kg). Given that Corrie weighed about 85kg confirmation bias may have come into play - the wrong figure was in the right ballpark
* Picking the wrong figure - Biffas IT might consolidate various data for a given Customer/Pickup and the wrong one was pulled off - say the actual amount of cardboard recovered
* Round/Route data changing. Given that there is some degree of manual process involved here it may be that we are looking at, say, Stop 2 on Round 43. But in the intervening period there were route changes - the horseshoe is now Stop 6 on round 45. So the wrong figure was picked up that way - which wouldn't have happened if the weight was recorded for billing purposes, and cross referenced correctly automatically on their IT systems.
I'm sure there's lots more ways things could legitimately go wrong, and the specifics of Biffas systems and processes will determine that. What I'd like to know is two things:
* Did the error involve just the weight, or the van/driver/bin too? Shireslueth had an excellent post a few pages back where he correctly pointed out that it wasn't just the weight which pointed away from corrie being in the bin.
* It seems that this new information is as a result of refocusing on the landfill, not the cause. So what was?
I think the most likely outcome of this will be that Corrie woke up cold, still wanted to drive home in the morning so got into the cardboard bin (the cleanest there). But it's still far from a certainty.