Having worked in the parts business on both the dealer and manufacturer sides, I can tell you that it is true that more than one part number may be assigned to the same part but not within the same product line. If an Edge spring has a different part number then it is different in some way from other Edge springs. But it is not uncommon for the same part to have different numbers across product lines - in this case an MKX part might be the same as an Edge part but still have a different number because they get it from a different supplier or some other reason.
One example I'll never forget... most Honda motorcycles use the exact same oil drain plug washer as Honda automobiles yet the motorcycle part number is different and more than three times the price of the automobile part. However, the Accord EX part number isn't different from the Accord LX number (or even from the Civic number for that matter) so the idea that part numbers change between trim levels for no reason other than pricing isn't the case. The ordering and inventory management issues alone would make that impractical but more than that, manufacturers wouldn't want customers to hear about such a practice which could be a violation of antitrust laws - and things like that tend not to remain secret for very long.