It might be more complicated than this . . .
I think the VINs are unique to the assembly line. (perhaps GD can confirm ??)
For the Reflections, these seem to come off at least two different lines, so there is no one sequential order to the VINs.
The build sheet permanently fastened to a wall inside a cabinet shows the day of manufacture. This might be a better reference to go by.
There is a VIN breakdown on page 2 of your owner manual. The numbers following the model year digit (i.e., "F"=2015) indicates the plant, line and the sequential build.
Example: F1102634
..............F = model year
...............1 = Plant
.................1 = Line
...................02634 = sequential build