Plate Markings Question

[BSimon999@AOL.COM]

I have a customer with a Mason and Hamlin console. The serial number paint 
marked on the plate reads MH 71126, with the MH being above the number. That 
equates to early 1968 according to the Pierce Atlas. 

Cast into the base of the Wickham made plate I found "Wickham", and "81, 6, 
and 21", with the numbers being above on another , like;

81
 6
21.

Can anyone tell me how to "read" the code of the cast numbers? 
( since they do not seem to intuitively indicate the year 1968 )

Thank You,
B. Simon
Phoenix