Perhaps I'm being a tad too stiff about it, then. Hollywood has always been fond of turning to best selling books and plays for movie subjects. Completely original screenplays are in the minority. Singin' In The Rain is one of those - it never existed anywhere before it appeared as a film, even though there's now a very cumbersome stage version. Calamity Jane and The Producers are also in that category - funny how so many of them are musicals.
On re-reading the above posts I can see where my distinction was maybe a little too fine; on the other hand, rather than just limiting this discussion to "Hollywood," it might be better to say that all literature (books, plays, films, TV, etc.) has enjoyed placing fictional (or "adapted") characters against historical backdrops: Les Miz, A Tale of Two Cities, and of course, Jeremy, the two you cited, Gone With The Wind and Doctor Zhivago (Lawrence of Arabia, The Bridge on the River Kwai, Mister Roberts, The Caine Mutiny, The Train, In The Heat Of The Night, etc., etc., etc.).
Cheers!
Roy