I've ordered down through Ayce,(thru-kiker) several times.
Give him a call and ask what the last batch of down fill is.
Ayce puts 800 fill, because you will get at least that.
Most of the time his fill order is around 830 but when he gets the 860 fill he orders more, so it will be available about 1/2 the time.
You can call 900 what-ever you want, but 100% of it will be 860.
I don't think they have there staff picking out the few feathers that come in it to make it 900.
In fact the down pretty much is 900 fill that you get. The few feathers you get with it are what bring it down to the 830-860 range.
Maybe that's why company's call it 900 fill. They just count the good stuff as the number and don't take anything off for the few feathers that come in it.
Ask Ayce, he'll tell you straight.
If you want to spend more for the 900, try also ordering 3 ounces from thru-hiker to see for your self, (it's all comes from the same batch).
If you think about it, a company that claims 900 fill can save a 1/2 ounce for every 9 ounces over competitors like Western Mountaineering. So why does WM only claim 850 fill? Because they're honest.
I would take a 900 fill companies claim with as much of a grain of salt as I would there claim to keep you warm at that bags certified temperature rating.