Duplicate Serial Numbers

Model numbers are not unique, but serial numbers are specific to that item. 
 

It isn't unusual for scammers to find photos off the internet--often from a closed sale transaction years earlier.  I was looking at an amp and had a bit of alarm, call is a mild yellow on my BS meter.  I google searched the photos, found them on an ad on a small audio site that closed 2 years earlier, and confirmed the scammer did not have the amp.  I pretended I wanted to buy it and got far enough to indentify her as a lady with red hair in Nigeria but was unable to do anything across international borders.  Use google photo search to see if the photos are elsehwere on the internet.  --Jerry

Spoke to the manufacturer. Was advised that the speakers look authentic and that it may simply have been an accidental duplication of serial numbers.

So the manufacturer confirmed that its serial numbers don't guarantee authenticity, because they can potentially duplicated for reason or no reason. 

What brand of speakers? Low end? I assume.

This is the mark of poor manufacturing practices at best. If there are actually two sets on the market which came to light by a random person (no offense to you)… then there are dozens or hundreds on the market.