BBY stands for Before the Battle of Yavin, and ABY stands for After the Battle of Yavin, while BBC/BBP or BC or BCE or BP stands for Before Christ and Before Present (Before Christ, Before Present est.) and AD stands for After Death.
Some of the factors that we are going to be looking at the timeline of our World History and what sorts of things that happened on the first date of Before Christ and After Death on the very first year.
The Gregorian and Julian calendar started on this very first day of existence on January first year of celebration for the year 1. According to the Julian calendar they do not approved the year of zero. So what happened on 1 BCE, there was an leap year on Friday or Saturday. Plus adding the birth of Jesus Christ in the religion of Christianity was born, in which it results so much exaggeration. The latest scientific evidence cannot claimed they identified Jesus Christ to get any such degree for their trace elements or clues of civilizations that left behind on Earth! With our human technology the only trace of that dated as far back during 1300’s with Jesus cloak and his clothing.
On the other hands using an galactic standard timeline standpoint from Star Wars what happens on the first day of ABY was an spark of Jedi Rebellion. It was when George Lucas created his first film of Star Wars “A New Hope” Episode IV! There are over an thousand of generations before the Jedi Rebellion that the dark Empire were threatened over the galaxy. The earliest date in the Star Wars expanded universe what they also defined The Force as a whole is 13,000,000,000 BBY, which serves as the year the universe was created. The way how it finished had reached over 134 years ABY. Plus over the course of galactic standard timeline it cannot be so well identified with Earth settlement of humans, because Earth was completely off the picture of Star Wars universe inhabitants.
The major events and coincidence happened on 1 BCE and AD cannot be identified with an Star Wars timeline for the spark of Rebellion. Only the World War II events of history can identified some meaning of Before the Battle of Yavin and After the Battle of Yavin although it cannot be so true, because of the words redefined.