I listen to my iPod in the car and sometimes a song will come up and I'll blurt out the year I think the song was released. Many times, I'm within a year or two as later verified by Wikipedia. My family wonders how I do that since I have over 11,000 songs on my iPod. They don't believe I'm magic or telepathic which is kind of a shame since it would really elevate my status in my family.
The answer is much simpler, actually. With a lot of the music in my collection, I can associate a song with a time period, a location or a person. I might remember dancing to the song in the high school gym or hearing it while driving to the mall a few towns over from my childhood home. If it's jazz, I might remember that I discovered the song while working at a radio station. All of these clues help me remember times and places and that makes it easier for me to narrow down the year I first heard the song.
I graduated in a class of 675 students in a high school that was comprised of kids from several towns. Yes, I came from a small town! What's great is that next year will be a big reunion and I hope to travel back 'home' for the event. I have many Facebook friends from school and we are spread out from coast to coast and many states in between. I have not seen many of my friends in years and I am truly looking forward to seeing them next year.
That, and hearing the old Classic Rock with the people who I heard it with first...when it was just plain Rock and Roll and the memories weren't memories at all.