Interesting. My 9/28/65 scheduled build VIN 112xxx SJ car is definitely red oxide underneath (pinkish/salmonish "red").
Yes have cars prior to this approx three week period, with the pale red oxide on file
Same here as Rockhouse66. 10/14/65 SJ with a 119 vin with red oxide underside. 6R09A
Since we kind of accept that the projected build dates can be off by possibly three weeks your car could easily have a projected date inside this batch colored floor but actually been built just prior or after putting it in the red oxide period
That's what makes this all so fun
Thanks all for the additional data points. Just thought I would mention that I don't always post full vin's since the examples I'm posting are not my cars but belong to others. Don't want someone goggling/yahooing their VIN and getting upset about details being made public.