Lol internet.
A B C refers to the generation of that particular density. E.g. Samsung had an 8Gb A-die. Then it got replaced by 8Gb B-die. Now it is getting replaced by 8GB C-die.
Meanwhile the second 16Gb chip became available and it gets called 16Gb A-die. (Yes second, because the first generation is "M" in Samsung's naming convention.)
That is all this is.
Would the current B dies clock faster than A and C? Maybe, because of newer design than A and more mature technology than C. Or maybe it doesn't (compared to C), we won't know until we get lots of C. But looking at the technical talk on the internet, makes me sleep well tonight.
P.S. It's lame to discuss performance in terms of A-die or B-die or C-die because the A-die of a smaller size is not the same as the A-die of a bigger size (The former would clearly be older in this case), and the first gen of a newer/bigger size could be using a similar or derived design of a second or later gen of an earlier/smaller size because they come out at the same time. But I see lots of internet talking about it this way.