In fact Ihad read that the ultimate acronym meaning was Before the Christian Era. Which made much more sense to me than “common”. Common what?
I have no idea. There is no “common” count of years—the Chinese have their years, Iranians have theirs, Jewish have theirs, and probably many other peoples have year count systems differing from ours. “Before the Christian Era” is just as good as “Before Christ,” and the fact is, that is the beginning of our year count.