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I also have an iphone 6s plus with serial number beginning with FC

2017 WEEK 41, still under Apple warranty, ends in a week.

There is ~1 month between mfr date and when the warranty begun.

I'd guess these are excess Applecare replacements that were repackaged in the US and sold discounted to various retailers. The retailer this was bought from still has them in stock, new iphone 6s plus
 
There is a small craftsman workshop in Fountain Colorado where Santa hand makes 1 iPhone each year. Congrats looks like you got it!

Not 1, 2. :) Week 41 2017 There's definitely loads out there just almost nobody cares enough to search what the serial number means.
 
Seems my iphone 7plus is also a FC

Nice Name: iPhone 7 Plus (AT
Machine Model: iPhone9,4
Please visit our facebook page
Family name: A1784
Model Number: MN5K2
Group1: iPhone
Group2: 7 plus
Generation:
EMC number: 3092
Model introduced: 2016
CPU speed: 2.3GHz
Screen size: 5.5 inch
Screen resolution: 1920x1080 pixels
Colour: Rose Gold
Production week : -34- (August)
Production year : -2017-
Model introduced: -2016-
Capacity: 128GB
Memory - flavour: Soldered
Memory - maximum total: 3GB
Factory: FC (Fountain, Colorado)
 
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