They were pickling Snokes that far back, when Vader was alive?
What they’re probably going to end up claiming is that the first successful Snoke wasn’t created until the time of the sequels. Probably the other Snokes were lacking in power or were straight up dead.
IMO, kinda sucks that they’ve focused so hard on giving Snoke a bunch of clones when in reality it should just be about Palpatine clones, and Snoke was their first lab experiment that went right.