Each day has a different number of vehicles the line can produce. I have not really checked anyone elses blend dates, but being first phase they are most likely scheduling light for QC.
The number in the upper right XXX/XXXX is the build order on the assembly line for your blend date. Bmend dates can change or be pushed, but the first number is your position, second is how many are scheduled for that day. Mine is 162/428 for today (4/20) but if yesterday's batch was not built...
On my Bronco, that happened the first time the day the truck was actually built. After it rolled off, when it went to the Mod shop, and when it shipped out the date always changed.