[Mr70]

To answer your question,Motor Wheels YA coded 14X7 Magnum 500 wheels were used on various 1969 models and also early produced 1970 Super Sport Chevelles-Elcos & Novas,before they switched over to the same wheel,now stamped AO.
So far as I can tell for the 1970 Chevelles-Elco w/YA wheels,Kansas City Leeds plant vehicles built as late as 11/05/69,and Baltimore plant as late as 11/20/69,were the only plants using them that late into new model production.
I've heard of some having wheels dated anywhere from a few days before their Vehicles cowl tag date,all the way back to 3-4 months before in some examples.