You are on to something. See below.

( Router Base )
( File created: Thursday November 22 2018 - 02:48 PM)
( for CNC Roter Parts Machines )
( Material Size )
( X= 190.500, Y= 190.500, Z= 12.319)
()
(Toolpaths used in this file
(Pocket 3)

I went back into Vcarve and my job size is in inches...... 7.5 x 7.5, which is 190.5 x 190.5. My runs on Monday were in mm, but no changes were made to any of the configs in Mach 3. Is it possible that Vcarve is still outputting in mm even though all indications are inches?