Through 1969 Chrysler used two-character paint codes (W1, B5, Y2). For 1970, the numbering scheme changed: paint codes acquired a model-year letter prefix (E for 1969, F for 1970, G for 1971, and so on) so that a color carried from one year to the next would be unambiguous as to which year's run it came from.
The transition was not perfectly consistent — some plants kept stamping two-character codes for a few weeks into 1970, and 1969-carryover colors on 1970 cars sometimes show the older format. Plenum's schema treats both formats as valid for early-1970 builds and flags a conflict only when the format disagrees with the build date.