Without wanting to sound smug or superior, I almost never get confused or mistaken about the release dates of things like films, albums or singles, or comics. I have a really keen sense of historical chronology -- at least as far as 20th Century art or literature goes -- probably because I'm a history fan generally. Dates tend to stick in my mind. I also have a keen sense of the conventions or styles of things like movies, comics or music over the decades. So identifying a piece of work's approximate date is usually pretty easy for me.

Again, I don't mean to sound smug, but that's the truth of it.

I remember being surprised that Plastic Man was published up through 1956. I thought it ended before the code.

Hard to sound smug when you are a giant green rabbit!

I'm also a history buff and can usually narrow pop culture down to part of decade, if not the year; depends on the subject.  Comics books I can get within a year or two; usually closer on stuff in the 80s, when I was collecting and had more steady access.  Before that, I can usually get it down to 2 or 3 year timespan, for the 70s, widening as we go back in my lifetime.  For Golden Age, I can usually get which half of the decade, and 30s, 40s or 50s.  I was looking at the newsstand feature at Mike's Amazing World, while downloading something, and was looking at the 70s, month by month and kind of recalling what I read newish then, vs later.  I didn't really have much access to comics until the latter half of the 70s, with my own money and mostly borrowed friend's comics, in the first half, apart from a few I received as gifts or skimmed at a newsstand.

Music I'm a lot looser, apart from 80s New Wave (and other 80s music), where I can get it much more accurately.  Books as well, though after 20 years selling books, timeframe of release can kind of blend together, unless it was very significant, like the 4th Harry Potter, which is the first one we had a midnight release party.  I can usually get decade and portion of decade, though it varies by genre.

For me, for things in my lifetime, it's usually a matter of associating it with personal experiences.  For instance, I can pinpoint comics of the 80s by recalling where I was in college, when they came out (or high school, for the early 80s).  After that, it is recalling in my professional career and what was going on when something came out.  For instance, I know that the Man of Steel Superman revamp came out in the summer of 1986, because I saw the first couple of issues when I got home from my Midshipman Training Cruise and went into local comic shops, in St Louis to look for comics.  I got a subscription going, when I got back to school, in August and there was a new comic shop, right off campus.  I can pinpoint The Greatest Batman Stories Ever Told hardcover to 1988, since I found it at a comic shop in Athens, GA, while I was attending the US Navy Supply Corps School, after receiving my commission.  That was also the same shop where I saw my first issue of The Tick (though I had a poster of him, which I received with some back issues I mail ordered from New England Comics).

I'm sometimes surprised by the month that something came out, as I occasionally think it was later or earlier in the year, until I look at the actual release date.

1983.

A gap in publication history that surprised me was the Riddler (although this is actually one that I learned about many years back). I had assumed that the core members of Batman's rogues gallery became regulars after they were introduced. It was a surprise to learn that after just appearance in the 1940s, the Riddler was put in mothballs for over 15 years. I also read recently (maybe in one of shaxper's Batman threads) that a period over several years in the 1970s when Riddler and a bunch of other classic Batman rogues all barely ever appeared.

Quite a number of Bat-villains were seemingly forgotten after making a couple of appearances.  The Riddler showed up twice in 1948 and wasn't used again until 1965.  The Scarecrow debuted in 1941, reappeared in 1943, and then wasn't used again until 1967.  Poison Ivy made two separate outings in back to back issues of Batman (well, they would have been back to back had a Giant issue not gotten in the way) and then appeared only sporadically here and there and even then, those appearances were in titles outside of the Batman family (ie. Lois Lane, JLA, Secret Society of Supervillains). 

Two-Face made one appearance in an issue of World's Finest (and even then, he was being impersonated by Batman) between 1954 and 1971, The Penguin vanished after 1956 and didn't reappear until 1963, and even The Joker took a hiatus between Dec. 1969 and Sept. 1973.