Star wars

I'm reading a lot of Star Wars fanfic right now, in particular fix-its (often time travel fix-its) set before the rise of the empire. And so, so many of them use "BBY" to specify the date. "BBY" stands for "Before the Battle of Yavin". None of the characters at this time know that the Battle of Yavin is going to occur. They should be giving dates in the Republic (or other contemporaneous) calendar.