The "golden" one is by owner "099720109477"
Looking at the community AMIs for that owner I see tons of Ubuntu, and one xenial - but it's PV, not HVM.
At one point, this was the "official" owning account:
http://ubuntu-smoser.blogspot.com/2011/07/how-to-find-right-ubuntu-ami-on-ec2.html
It's the same owner for the ones listed on
https://cloud-images.ubuntu.com/locator/ec2/ so I guess it is the same stuff.
What confuses me is I cannot locate the AMI from the quick start back at the cloud-images site, and it appears to have a complete history.
Trusty LTS HVM SSD: ami-fce3c696
AMI Name: ubuntu/images/hvm-ssd/ubuntu-trusty-14.04-amd64-server-20160114.5
Appears the same for Xenial is ami-840910ee
AMI Name: ubuntu/images/hvm-ssd/ubuntu-xenial-16.04-amd64-server-20160420.3
Maybe that is the reason - the new trusty is 20160114.5 and is not on the list (perhaps the list isn't getting refreshed with minor updates)
I think this exercise proved the point I was hoping to figure out.