[Mr70]

In general,here's a typical breakdown on some SS rims I have here.
To the far left of the valve stem is the manufacturer & plant and last digit of the year it was assembled...M1/9<--(actually under the line),stands Motorwheel,Romulus plant,1969.
To the right of that is number for the month assembled from 1-12..12 is for December.
To the right of the valve stem is another number for day of that month..15 for the 15th.
YA or AO code following that stand for vehicle application it was intended for..i.e Chevelle-Elcamino/Nova Super Sport.
Breaks down as 1969,December 15th that this ENTIRE wheel was assembled as a complete assembled unit.

On the inside barrel itself.. 14x7 JJ M1 9
14X7 is the rim size.
JJ is the rim contour of the wheel.
M1 9 for Motorwheel,Romulus plant,1969.
Sometimes you'll find a small number under the 14x7 indicating month that part was made,and a letter under the JJ indicating early or late production for that model year.
This is JUST the barrel production date stamp,and not the overall wheel completed date as above.