Why are Part numbers of some PMA aircraft spares the same as OEM and other PMA parts are slightly different?

Question

Why are Part numbers of some PMA aircraft spares the same as OEM and other PMA parts are slightly different?

Answer 1

Different parts.

Answer 2

Different mods (modifications) of the same part will have different part numbers, and you must be sure that the aircraft you want the part for is eligible to use the specific mod part you have in stock.

Answer 3

Kind of like (but for different reasons) an MS20470AD4-4 rivet is the same as an AN470AD4-4 rivet.

It is a way of marking the part which resembles the OEM part, but identifies it as made by a different manufacturer.  This is for internal numbering for the PMA manufacturer but doesn't look completely foreign to the mechanic that ordered it (I asked for a XXXX-XX not an DXXXX-XX!)

For example, an OEM part number might be 45389-4 and the PMA part number might be AG45389-4 or 101-45389-4.  Typically the dash number will be the same since it identifies the size or type of part.