About two years ago, we spoke to FNMI, and a VP replied that FN is contractually prohibited from selling ANYTHING they make in their South Carolina plant to ANYONE except DoD.  FN does not, and has not ever manufactured flattop uppers.  They have the contracts for the M16A2 and M16A3, and have also had M16A2 upgrade contracts.  They make no AR15 parts, as they are not allowed to sell AR15s or parts commercially.

In MOST cases, people marketing parts as being made by FN is totally bogus, but it's easy to get away with as it isn't something that most people can easily verify.  Plus, there's a built-in distraction mechanism, as most people think that Colt makes all the M16s, and are surprised when told (correctly) that "FN is the current manufacturer of the M16 for the US military."  That new fact makes most people forget to ask "so how do I know that these parts are actually made by FN?"

Beyond that, FN does subcontract out for many of the parts that they use, as do all the AR manufacturers.  While it is certainly possible that some of the alleged FN parts are coming from FN subcontractors, that does not mean that the commercial parts are being made to the same specs or the same levels of quality control as the ones supplied to FN, nor does it mean that you can correctly call them "FN parts."  Only parts accepted by FN (which are then locked into sales to DoD) can be correctly called FN parts.

Now, once DoD receives the parts, they can do a number of things.  They can (or rather, they formerly could) surplus the parts.  They could also give or sell them to police departments, usually via a police distributor.  They could "lose" the parts (i.e., not take them home after a deployment), or the parts could be stolen.

Parts could also be submitted to FN from subcontractors, be rejected by FN for failing to meet QA/QC standards for any number of reasons, and then sold as "scrap."

Unfortunately, there's no way to prove the source of a given part, especially one not definitively marked.  But it IS true to say that the amount of true, in-spec FN parts in the civilian market is quite small, and that most parts marketed as being FN parts are not, in fact, FN parts.

Does that matter to you, the buyer?  I dunno.  For a range gun, probably not, if it works.  But if you are talking about a duty gun or a defensive weapon, I would recommend against "unknown" parts, and stick with parts whose pedegree can be established.

Of course, YMMV.

-Troy