I find it very understandable how discrepancies can appear in any written work over time. As an example of circumstances, back in my early days on BR, many people, myself included, kept a personal record of things we were taught, or had to remember for the benefit of the job we were doing, and by this I mean things such as siding capacities, train movement scenarios at terminal locations (ie: if a departing train from Waterloo was leaving platform 9 - or lower - toward the Down Main Fast, then a simultaneous arrival in to p10 or higher could arrive from the Up Main Fast. But if the said departure was from platform 10 or higher, the simultaneous arrival would need to arrive via the Up Main Relief). That may seem inconsequential to many, but within the detail that had to taken in to account for the peak hours at Waterloo, it could mean the difference between a reliable timetable and one that was regularly a victim of late arrivals or starts. This sort of information was never kept in some central store, it was more often than not just 'known' by those directly involved, or noted by some (such as myself) who were interested in same.
In more recent times, with the introduction of computer systems, much of this 'detail' has been written in to official internal documentation. That is all well and good, but the sheer volume of such detail for any given location on the railway, can be immense, and the upkeep/updating of same has, I would guess, become a whole industry within an industry.
In my later days, there were some departments (non safety critical I should add) who would issue similar work threads, with updates of their activities etc, that after a few months the updates would drop off a cliff with no explanation, and one was left to assume the associated workload was simply too much for the staff to upkeep.
In a similar fashion, keeping written works (books and such) completely up to date over several issues, will not be an easy task. Having had to do same in the course of my career, I would not want to be going through that process again in my retirement !