Why O&M manuals arrive late and incomplete
The information exists. It is just scattered across a supplier's inbox, a subcontractor's PDF and a spreadsheet someone left behind when they moved on.
So the manual gets built at the end, under time pressure, by whoever is available. Gaps get filled with whatever can be found rather than what was actually installed. The client signs it off because the alternative is delaying handover, and two years later nobody can tell which valve was fitted in which riser.