Today’s the day
It’s the day!!
He definitely did, but since the whole book is supposed to be a translation of something he found and not something he personally wrote, they’re switched for the audience’s convenience. There’s a lot more to it, but here’s a chart of Shire months from the appendices at the end of RoTK. Elves and men are different, but there was no handy chart.
Happy… [squints] Winterfilth, everybody