I find that when working with time, I get a lot better results when I use JS Date objects, and then let Plot work it’s magic (with a bit of help from it’s console messages).
I forked your notebook, and changed 3 things:
Converted the year column to be Date objects representing January 1st of the given year.
Switched to a rect mark instead of a bar mark and set an interval, as suggested by Plot’s warnings.
In the second chart, I show how you can approximately customize the number of ticks.