OK, another example, I have a 1973 340 here I just looked at, it says;
?W 340 R 4137 8126 (first digit is not readable, but it has a 1973 VIN)
The 4137 is the 10,000 day calendar date code for Nov. 24, 1972 (1973 model year)
So it appears that both types of date coding were used.