[Mr70]

Yes it is a 1969 application,but your cousin could have possibly found that on a early built 1970 Super Sport too,(Sept.69 to late Nov.69 from buildsheets I have)
Although built nearly a year prior,I would imagine they used up all the remaining YA coded inventory before the AO coded wheel was tapped.I did see a early 1970 SS car with 12/27/68 YA rims,& looked to be authentic.
A.Colvin states the earliest assembled AO code he has seen is Sept.23,1969.