Well, I wasn't able to get to the Big Drill today, but I did just spend a few minutes on that 1mm... :-D.  It was nagging me all day...  I did a quick analysis as to why it wasn't the same on both sides and I couldn't really see a good reason other than it needed a little more encouragement to move back on the right.  With a strategic slight push on the right side's door frame.... and they were perfectly the same on both sides.  50mm from the 6th rivet up to the window frame edge.

I'll sleep better tonight. ;-)  Hopefully I'll have a couple of hours in the morning to start drilling.