Tom, as you said, Frigidaire introduced the "Tender-Matic" feature instead of the meat thermometer in the 1965 Flair and free-standing ranges and it continued to offer it for 1966-67 while the meat thermometer remained in the built-in ovens. I have that Tender-Matic feature on my newly acquired 1967 Custom Imperial range and I haven't tried it yet! I just got the instructions on how to set it... I have to admit that I'm more curious to see how it works than about how well it works!
Right now, I'm working at fixing a 1960 Custom Imperial 30" range that I got for free locally. Strangely, the 30" model lost the meat thermometer in 1960 . In 1961, the feature was back but the "broiler grill" (adjustable broiler) was missing and the broil light was now gone (but that was still there for a few more years on the 40" model). In 1962, the broiler grill was back but the oven now had a regular door and the burner controls were now regular round dials instead of the "radio dials" which stayed for one more year on the 40" models.
As for 1965 vs 1966 control panels, the main differences between both years was changes of colors on the control panels. They got taller for 1967 with a redesigned clock and relocated burner controls.
Here's a timeline of 1964 to 1970 Frigidaire 40" Custom Imperial ranges. The control panels got taller in 1967 and again in 1969.
Pictures
#1-2 showing a 1964 RCIG-75-64 (has a meat thermometer)
#3-4 showing a 1965 RCIG-75J (first year for the "Tender-Matic" and the "Meal Minder" features.
#5-7 are from a 1966 RCIG-75K (the only year for two windows in the oven doors of the regular free standing range)
#8 is a 1967 RCIE-75L (first year for the Electri-Clean version of the 40" free standing ranges, taller control panel)
#9-10 are from a 1968 RCIE-75N, that year, the "Tender-Matic" was gone and the self-cleaning system was simplified.
#11-16 are from 1969-70 RCIE-75P which got taller control panels again.
