Previously, finding superseded numbers was accomplished using the "COS" - Canceled Obsolete Superseded - Parts List publications:
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The Master Parts List (MPL) publications can also provide some information:
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The Accessories Parts List (APL) is also helpful for the Mopar retail lines and other areas:
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These publications were generated mostly annually, with supplements filling in. It's digitally handled today. Dealers can see supersession history in part number look ups, but these are what they could have used in the past, although computer access to dealers has been available since the 80s. Paper publications might still be available in some cases.
By the way, if you ever wondered what the "NS1" code or similar NS and others meant when a part is no longer serviced, the COS describes them:
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