Yeah, this is just wild to me that they would use different bolts for the same application on the same car, but I know this was a fast moving, use everything process, and the early February 10th build date seems like it coincides with the switch to the star head washers as you have stated...
Sorry that is not what I stated Plus the Feb 10th date is purely a guess since we don't know when any of these cars were really built. Saw your post over on the other site and I hope you correct that there also
The projected build date for the example I have here at home is the 9th of Feb and it had the stars. Just checked their on both sides and they are stars on both sides
But the chart below should give you a fairly good handle on the question your first asked "I'm wondering if anyone has any shots of or know what the window track/guide bolts and washers looks like on a February 66 San Jose car at the back of the door by the latch"
Without looking at all my pictures I found the following
6R10153x - Smooth
6R10170x - Smooth6R1050xx - Star
6R1124xx - Star
6R1137xx - Star
6R11631x - Smooth
6R1174xx - Star
6R1201xx - Star
6R12225x - Smooth
6R1225xx - Star
6R1253xx - Star
6R12710x - Smooth
6R1296xx - Star
6R13773x - Smooth
6R1439xx - Star
6R1488xx - Star
6R1524xx - Star
6R1590xx - Star
6R1611xx - Star
6R1639xx - Star
Your car
6R17199x - Smooth
6R1725xx - Star
6R1797xx - Star
6R1857xx - Star
6R1875xx - Star
6R1980xx - Star
6R1991xx - Star
6R2031xx - Star
6R2088xx - Star
6R2165xx - Star
6R2283xx - Star
6R2309xx - Star
6R2313xx - Star
Looks like 6R17199x might have been built out of sequence by a long shot (more than the expected up to three weeks spread found between cars being finished on the line) VINs place it three months between it and the last smooth example in the search. Or an odd/old box of hardware got mixed into the rotation to that station somehow.
Agree with your choice of leaving them. But be prepared if someone asked how you'll explain it
Need to take this, since we spent the time to collect, into one of those 66 Mustang Surveys I did earlier in the year.