Covenant; you're getting a little off track. Back to basics and keeping it simple. Your trimmer is fine and works exactly the way it should.
The Headspace of bottle neck cartridges is measured from the base to the shoulder. Your resize die should be setting the neck back to 0 SAMI specs. Just because you run you brass through a full length die does not mean the are resized back to Zero specs. I would suggest you get a Micrometer Gauge like the RCBS or MCS. The first thing you need to do is make sure your brass in uniformly resized because if it's not your trimmer will never be consistant.
The manufacteur or head stamp dosen"t matter when the brass is resized because all the outside dimensions are the same.
Be uniform in your resize operation and your problem will go away.