Model coding in effect from 1962 to 1981 and revised 1981 through current.
The current 8th position coding also applies to some other WP-produced brands. It repeats on a 19yr cycle. Move the 2010 X line up to the 1991 X line, 2011 then is Y and so forth. 2029 is the next X if the pattern isn't revised anew.
