A Place In Time

If I wrote a Western set in1877 that had a bounty hunter handing over a prisoner to Wild Bill Hickock - I imagine that I would get a pile of letters telling me that Hickock wasn't the law in Abilene at that time.
Same would happen if I had a journalist covering the battles of the Ameican Civil War with a portable typewriter on his back - or that The St. Valentine's Day Massacre was carried out by gangsters armed with Uzzi machine guns.
So, why is it that some authors today make that sort of mistake today?
It's a small mistake but the number of times that I have come across it is getting riduculous.
I refer to two small four letter words that begin with 'F' and 'C'.
Now, I'm no prude - any book set in the 1960s to the present day that use those words I do not have a problem with.
But when those two little words turn up in a western or a book that is set in the decades forward to the Sixties - it kind of jars with me.
After all if those two little words were in common usage it would be reasonable to assume that the likes of Mark Twain, Owen Wister, Ernest Hemmingway, John Steinbeck, Jack Kerouac and Raymond Chandler would have used them in their books.
The thing is that until the publication of D H Lawrence's ' Lady Chatterley's Lover' in the early Sixties those two little words were virtually unknown.
The thing that gets to me that a lot of these books have been researched but, not with the authentic language of the time. In everything that I've read about The Battle Of The Somme I never heard anyone mention '....the mud in the f...ing trenches....' nor, in the 1950s, did Derek Bentley standing on a factory roof say: 'Let 'im f...in' 'ave it.' So, if they didn't say it - why should modern authors say it.
Just keep the books in their place in time - maybe, I'd read more.