Quite a few of the so-called "professional" deck building publications I've glanced at over the years contain erroneous information. For exterior construction exposed to weather and water, using double-backed joist hangers is frowned upon because conflicting multiple hanger fasteners could weaken the beam and hanger stability over time. If you are going to use a center beam (I think what you are calling a header), your deck will be considerably stronger and easier to build if you install the beam below the plane of the joists, then support the full-length (14') joists on top of it. Continuous construction, in round numbers, is about 25% stronger than simple span construction.
Chances are you will have to buy 16' joists and cut them down to the 14' length, as few places today sell 14' stock. A better way to go would be to use the full 16' members, cantilevered 2' over your outside beam as well as resting on the center beam. Doing so will make your deck 15% larger without wasting so much material.