If they used shoddy methods for converting the dates prior to Japan converting to the Gregorian calendar in 1863, then it's absolutely relevant to their claim a

If they used shoddy methods for converting the dates prior to Japan converting to the Gregorian calendar in 1863, then it's absolutely relevant to their claim and could undermine their normalized trendline. If the dates are consistently 1-2 weeks off because they used a poor method for converting historical Japanese calendar dates to Gregorian dates, the line they drew normalizing their data would change significantly, and the BBC wouldn't have an article worthy of a headline. I don't understand why so many people are dismissing the calendar issue and just assuming that "it's accounted for" or "it's not relevant" or "it's trivial" or "it's just noise". Where's the transparency? They've shared their dataset, but not the method used to determine the dates? That looks like a huge oversight and so many people here seem to be accepting the premise of the claim and giving the benefit of the doubt to the researchers. What's scientific about that?