Not positive but I think I remember someone saying Amazon doesn’t include the fba charges

Your 1099 includes only sales that shipped out from 12:01 1/1/2015 2015 through 12/31/2015 @11:59 pm. Your first payment report of 2015 probably includes shipped sales from the end of December 2014. Your last payment report of 2015 probably ends before 12/31/15 and therefore misses some shipped sales included in your 1099