I suggest they have a Warranty registration page for owners on the web site as most others do.
These can also be updated in the case of a sale to another owner.
I’m sure they will not quibble over a day or so of actually taking delivery.
I would guess for example that with the batch going out now, the Warranty would most likely start from the month and inclusive of whole of December, and not necessarily the exact day.
From what I have seen and heard of the founders and Team, they probably will not split hairs over a few days.
Pieces of paper can be lost too easily and are a sign of inefficiency in this age of technology.