Great hat but what’s with the comma?
My thought as well. Comma is spurious.
The comma is to prevent the type from being mis-read.
With no comma, some would think it said January 202017.
The better solution would have been to allow one additional space between the numbers; January 20 2017.
Or a slash separating all three words; January/20/2017.
Sometimes, a typesetter only gets one chance to make decisions before the product is out of your hands.
I know this from experience. I used to illustrate for news ads.
Separates his Title and Office, from his first name.
It's an archaic practice formerly known as "proper grammar and punctuation."