Why, in old books, are dates often given with the years redacted?

Austen, Bronte, and others used this device also for names of people, places, and even regiment names (Austen). Why would they do this? To avoid accusations of inaccuracy (perhaps the author is taking liberties with historical facts for the purpose of the story), or even libel. I found this on a google answers forum:

It's also a fall-out from a literary convention of the time when many books and pamphlets were written criticising the government of the day, or important figures, by using false names. [Swift]'s Gullivers Travels is possibly the best known of the earlier ones. Since the reporting of Parliamentary discussions was banned until about 1808, it had to be reported in newspapers under false names (and Samuel Johnson first did it by reporting the activities of the people of Lilliput!). Some rather scurrilous stories were also printed which were thinly veiled parodies or criticisms of important figures.

I would also agree that with redacted dates, this would avoid tying the story to a particular time; obviously that becomes less effective as the centuries pass.

Some (cheap?) writers still do similar things. For example, in one book of a German “mass production” author, the following dialog takes place:

“Where are you from?” she asked.
“I’m from …”, and he told her the name of the city.

When I read this I was taken aback by how clumsy that sounded (in particular since this information played absolutely no role later on). And yet this style of obfuscating place names permeates all his books.

The most plausible explanation I could think of was that this should make the books seem “more intimate” because their lack of precision could place them in which ever city the reader was coming from.

The rationale is essentially the same as your conjecture that years were redacted “not to make the book seem outdated” so I would support your hypothesis.

I think this is merely a convention of fiction, which doesn't happen to be common any more. It may be, as some have suggested in comments, that it is a device that makes the work appear more like reportage.

In Gödel, Escher, Bach: An Eternal Golden Braid, Douglas Hofstadter spends several pages considering the translation of a single street name from a Russian novel (Crime and Punishment I think, but I may be misremembering). The street name is given as an initial, but he states that in this case it would have been obvious to anybody who knew St Petersburg which street it was.

If Hofstadter is right then in that case the device was used to remove specificity so the author did not commit himself to that particular street but anybody in the know would realise. But often (as with years) it does not appear to be hiding a specific year, but on the contrary suggesting to the reader that there is a specific year even though there need not be.