What leaves with the outgoing cleaner
The route order and why it is that order. Which gate is used and at what time. Which office is occupied late. Which floor waste dries out. Where the spare stock is actually kept as opposed to where it is supposed to be. Which contact answers and which does not. Which forklift route is active during the attendance. None of that is in any document and all of it affects the shift. All of it affects the shift and none of it survives the departure unless somebody arranges otherwise.
Some of it can be written down during the handover and some genuinely cannot. What matters is that the incoming cleaner has worked the building once with somebody who knows it, because that transfers far more than any written instruction. The written update captures what can be captured; the shift transfers the rest through doing rather than reading. The shift transfers through doing what a document cannot transfer through reading.
