Dodge Demon Gage Cluster question 1971 vs 1972

IIRC my '72 Demon , ordered new, did not have a seat belt light. So , I was surprised when I bought my second one '72) a couple years ago, it did have. Also my second one had cutouts in the trunk lid for mounting a spoiler which was not available in '72. IMOH I think Chrysler used anything left over at end of a years production for the next year if not substantially detracting from that years model.
Although I could be wrong.
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