I’d cut him some slack on this. I always screw up centuries, so I generally refer to years like 1700s so I don’t have to figure out on the fly whether to add one or subtract one to see if the Revolutionary War was in the 18th or 16th century.
I do the same and if I DO refer to the 16th or 18th century I alwasy have to stop and remeber if you add 100 or subtract 100. Not a big deal.