It would be interesting to put a time machine into the factory and see just what did go on.
Yes, barrel date is supposed to be installation, but I am willing to bet 50 cents that hey tried to stay ahead of things and dated 'em up a bunch in advance. So along comes January 2 and they have a pil of barrels dated 2 days ago ("last year"). What to do? Send them for scrap? Or use 'em up in the next week or so?
Consider the forging, the drawing, the turning, the straightening, drilling, boring, reaming, FORTY passes down the rifling-bench including EIGHT hand adjustments of the Box-Cutter, gauging, chambering and inspecting at each and every stage...... Are YOU gonna trash it because it's dated 2 days ago?
I have run into this before. To me it says a January rifle, but I could be wrong.
Hope this helps.