When DC "rebooted" a lot of their heroes in the 60's, they gave some of them different identities, origins, and even different powers.
For example, the original Green Lantern (Alan Scott) got his power from a lamp and its weakness was wood.
But the second Green Lantern (Hal Jordan) got his power from an alien and its weakness was yellow.
To resolve the differences, at some point they got the idea of multiple universes (and multiple earths).
The original "golden age" was from "Earth 2" and newer heroes were from "Earth 1".
Of course some of the heroes were the same person on each Earth, such as Green Arrow (Oliver Queen).
I don't know enough about Green Arrow to tell you what the differences between them were, but most of what you've read is probably the Earth-1 GA.
But Black Canary, that's even a bigger mess.
Then in the 80's, the series "Crisis" was supposed to resolve and eliminate the different Earths... and since then there have been other stories which seem to have made things even more convoluted.
But I hope I helped a little bit.