If you read an old novel or news article, they always use dates like 18–, or Mr. G----
Why is that?
Welcome to the board.
This is about the third time someone has asked this question this week. What are they assigning for summer reading this year? 
In any case, putting in the blanks is a convention to indicate that the author is talking about a real person or date, but is trying to disguise it.
No cite - but if I recall rightly, the explanation is that when the novel first started appearing as a literary form, authors used to pretend it was a real narrative, and so put in fake disguises of attribution.
**Les Miserables ** by Victor Hugo did this. Well, not with dates or names but more locations(at leasy my copy does). It will talk about a small town and refer to it as M- s- M- or talk about the “Bishop of D–”
Have you never heard of “fill in the blank?” Does the author have to do all the work? 
I’m re-reading Catch-22. Who could forget Major ------ de Coverly?
In this case (not analogous or even relevant to the OP, I know) the narrator explains it as part of the Major’s mystique. No one knows who he is, who he reports to, what his duties are, or even his first name.
Of course, we never learn the first names of the vast majority of the characters in the book (Joe Yossarian? Bob? Jim?), but Heller’s use of the “--------” highlights the fact that Major de Coverly’s first name is unknown to everyone.
It does create the problem of pronunciation, even in one’s mind. I always thought of him as Major Blank de Coverly.
That’s one way, I suppose. I mentally “pronounced” his name with a long pause there.
“Should I marry W.? Not if she won’t tell me the other letters in her name.”
- Woody Allen
The reason for not entirely specific dates is to keep the book from becoming stale. If you give a somewhat specific date, such as 18-, you’re story will seem timely for the rest of that century. The reason for not entirely specific names varies a bit more. Sometimes it’s for the tingle of a “blind item” and other times it’s to avoid mentioning something specific and get embroiled in god knows what.
I’ve always found it interesting that, in so many cases, inflation was such a non issue that writers feel free to give specific sums. (e.g., “An income of 47 pounds.”)
What are some old novels that give anonymous dates? I’ve only ever seen it in science fiction.
Actually John Irving does this in The Cider House Rules also.
Interesting.
“The Plague” takes place in 194-
In “Crime and Punishment”, Raskolnikov’s mother writes him from the province of R-------.
Actually, it’s John Yossarian.
This isn’t confined to old novels, either. In Carol Shields’ The Stone Diaries, published in 1993, there’s an obituary that begins “Peacefully, on --, in the month of – in the year 199-.”
One book that does this alot IIRC is Sherdian Le Fanu’s Through a glass darkly a book of short horror storie spublished IIRC just before the turn of the century. The reason for this is clear is that the author is presenting the stories from the files of a doctor and therefore is suggesting that they are true stories.