Link on the net to decode SS Chevelle ? wheels????

[Mr70]

YA was the 1969-early built 70 application.
AO was the one that followed it in 1970.
You are correct on the month/year decoding.
Look for another code to the left of the Valve stem and month code that will narrow down the year.
Looks like M4 with an 8,9,or 0 under it,
Decodes as 1968,1969,or 1970.
This helps determine for example,if it's a YA October 1968,or October 1969 rim.