The 5 in the 1J5 just means it has silver dials, the 920 means it's canbus, the 4 in the 946 means it's full fis, the C on the end means they're a 160mph dials and the 6 means they're immo 3.
My clocks are 1J0 920 946C, not sure if it's just based on the part number though or if there's like different eeprom versions.
Anyway I should have the eeprom for my clocks around somewhere if needed.