A quick look at "Mustang Production Guide, Vol 2" for 67 San Jose shows a "scheduled build date" of 27B (a Thursday) for 7R187130 and 006C (a Monday) for 7R189062, with dates 04C and 05C to be a weekend. Those VINs fall inside your "no" 7R186958 and "yes" 7R189290 cars.
Are you looking for a "closer" date?
Jim