What mistakes have you found over the years? I'm guessing they are sadly very common?
My pet Wrong Railway Fact is the date when the Merseyrail electric services started on the Kirkby branch and the Wigan Wallgate-Liverpool line was severed at Kirkby.
Many publications say this happened on the same day the Liverpool Link opened and Northern Line trains began to run into Liverpool Central (2 May 1977). While this was undoubtedly the original plan, some sort of delay meant the third rail infrastructure to Kirkby was not ready for the Link opening.
DMUs from the Wigan direction continued to run as far as Sandhills for a number of months after Liverpool Central re-opened, turning back in the reversing siding there. (I have memories of waiting in the cold and dark at Sandhills for a connection towards Wigan, having left Central not long after 5pm - making it autumn or winter of 1977).
A few sources do acknowledge the Kirkby electrification didn't open on schedule in May 1977, stating that it started in January 1978 to coincide with the Liverpool Central - Garston line re-opening (the Garston trains ran through to Kirkby and vice versa in the timetable back then).
Again, I don't think this is 100% accurate. On personal experience (with no hard evidence to back up my memories) I recall changing into Class 502 EMUs with destination Liverpool Central when the Kirkby "split" first came into effect. And in the reverse direction, boarding an empty train which was starting its journey from Central.
After making several of these trips, my connecting EMU at Kirkby suddenly began to show destination Garston. So I suspect the Kirkby electrics actually started sometime late 1977, a little before the Garston line re-opened. I can find nothing to confirm this in print or on the internet. If anyone knows the truth, can you let me know? (The BR Signalling Notice for splitting the line at Kirkby would be pretty definitive) .
Books are always well researched, right?
When it comes to Railway History, there are books . . . . and there are books!
Books written "Back in the Day" (say, the heyday of Ian Allan and David & Charles), I'd say are generally quite reliable (not always - I do take some of O.S. Nock's prolific offerings with a pinch of salt). But I think from the 1990s onwards, when the volume of railway nostalgia books ballooned, things could become quite dodgy.
I'm assuming the increase in titles and publishers was due to the appearance of easy/cheap desktop publishing, plus (forced early retirement / redundancy being rife at the time) a surplus of active late-middle aged blokes with a bit of time on their hands, access to collections of unpublished photos and an urge to knock out a book or two. And another cohort of geezers (like me) eager to buy them, usually on-line, even if some of these were badly formatted and laid out, with proof-reading and editing errors scattered through the text.
A good fraction of these books were based on a collection of photos of (usually historic) railway scenes, each accompanied by a sometimes lengthy caption. I won't mention any names to protect the guilty, but some of the books which cover my own area of interest contain some real bloopers. To the extent I think - if he got all this wrong in the areas I know about, why should I believe anything he says about somewhere I'm not too familiar with?
So, to the OP's original point - there's no shortage of Wrong Railway Facts to be found in books, and you need to be careful in choosing your authoritative sources.