Should I be using the date of the compilation instead?

Nope, go for the original year or nothing at all. It's not a big deal with the compilation coming out only a few years after the original, but when you listen to older stuff (e.g., 1930's jazz), then it makes all the difference in the world. I look down at the year field all the time and it's cool to be able to place all the music into a historical context.

Jazz labels tend to give you all the bibliographical details you could ever want. For recent pop labels, the best bet I've found is to dig around on the web for discographies of the band in question.