Complex sentence: The reason the mix is considered as such could be that it is a 1967 song featuring a Davy Jones vocal that was re-recorded in 1969, or maybe because it had been remixed prior to release.
Split into simpler sentences: The reason the mix is considered as such could be because it is a 1967 song featuring a Davy Jones vocal that was re-recorded in 1969. Or maybe because it had been remixed prior to release.