ZJ versus XJ emissions label on the firewall?

I always thought the ZJ was for the Grand Cherokees???

I just discovered that my 2WD, 1985 gas carburetor, 4 banger, manual Tranny, 2.5 L rig, that was converted 20 years later to a diesel with an SD-22 Nissan from a 720 pickup truck, has a

ZJ emissions label on the firewall???

WTF is up with that???

Not sure that has any meaning beyond maybe emissions. My 2.8 had SL on the emissions label.


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Some time back I saw another thread on the same topic. A ZJ in that location does not signify a mistake.