Of course there is, one only needs to specify which calendar one is using when giving the answer. You could answer in the Chinese calendar if you wanted. I'm

Of course there is, one only needs to specify which calendar one is using when giving the answer. You could answer in the Chinese calendar if you wanted. I'm trying to describe this without antagonism, forgive me if I fall. But your question to me sounds just like saying, "at what temperature does water freeze?" and claiming there is no answer because Fahrenheit and Celsius both exist. I feel like the article makes a similar mistake in claiming that certain dates did not exist. They are simply different calendars and the dates existed even if no one called them that date when they happened. It's like saying the 4th of July, 1776 BCE didn't exist - of course it did but nobody called it that at the time.