Just doing my lessons I came across the explanation of BC. It says
Remember how 紀元後 is “After death” or “AD”? Well, this is the opposite because it has a before (前) in it. It’s BC or Before Christ.
Wouldn’t that mean that there was roughly 33 years of missing between the date Jesus was born (marking the end of BC) and the date he was dead from where the AD would start?
English isn’t my mother tongue but I always understood AD as Anno Domini which is latin and means something like years of god.