Well, they all sound different regardless of year due to wood combinations, string choices, and electronics settings, etc. That said, they all sound distinctly Alembic.
I’ve played Series I Basses from each year 1974 to 1980, as well as a 2015 Series II. The 2015 was more hifi sounding than the older basses, that was the biggest difference I noticed. The 1974 bass had a very unique and beautiful sound, what I hear in my mind as quintessential Alembic, but that’s just my preference. So as I hear them, newer ones are more hifi and older ones have a more classic tone, but they all sound like Alembics.