Bill, the only thing I would add to this is since 2009, I have now documented three cars with what, in my professional opinion are original spare tires to the car. All three were March wheels and April dated Polyglas tires. The original owner guy has stated to me many times that the spare is original to the car. He has the car shipper with no mention of PL4, PL5, etc. The first car that I saw with a Polyglas spare was a few years ago and he had no paperwork. I have no reason to believe that is was not original to the car. What I sense here is a trend that Polyglas tires did make their way on to the 1969 Camaro. That's all. I'm not saying that thousands got them or 10 cars got them..........only that I have found, what I call three credible cars with original spare tires. John Kelsey can go into more detail about this. He's been in the tire business for most of his life and I regard him as an accurate source for the hobby. I have no connection to Kelsey tire. I'm only trying to post research data as I find it and answer the original question that was posted on this thread. That's it.
As we know this Camaro hobby can be a humbling experience as we are always learning more as time goes by. Case in point, the two survivor Z28s with mis-matching cylinder heads that I inspected two years ago. If you would have told me that Flint engine built a 302 with one #186 head and one #041, I would have stated I don't think that is possible. But now that two survivor original cars have been found with mis-matching heads, it appears that Flint engine did do this and probably not by choice at the time.