Less 'not so simple' than you think
"1st of January 1600 was the new year up North.
Must have been a bit confusing for the King, sitting on his throne in London Town, receiving a letter from Edinburgh.
My Lord you have received a letter from the plebs in your other kingdom, it seems they don't know what year it is."
Well in1600 the person sitting on the throne in London was actually a Queen (Elizabeth I). And of course Scotland wasn't 'her other kingdom'. It wasn't until 24 March 1603 (conveniently one day before the end on the year in England) that King James became king of both Scotland and England. As he had been king of Sotland for 36 years before he came to the English throne, he would have understood the strange Caledonian practices. And since he was James i in England and James VI in Scotland I don't think a little mental arithmetic when it came to dates was going to worry him,