[RS_COPO_Canuck]

The longer codes you posted that start with MD are later or could be re-pops.
Early 70 and earlier were 7 digit.
Later in 70 - an 8th digit was introduced.
Somewhere in 72-73 a 9-10 digit code became standard.

So....

5)A3NL L8CO - doesn't work with the below
6)LEO2G51 - 1968 - November


These are for pre 1972-73
First digit
M or Z =66
K or Y =67
L or T =68
J or U =69
E or W =70
H or X =71
G or S =72

Second digit
T=Jan
U=Feb
F=Mar
S=Apr
Y=May
N=Jun
P=Jul
A=Aug
C=Sep
K=Oct
E=Nov
R=Dec