Using index marks and shims is just another way of doing the same thing. Some of those nuts are aluminum. It probably isn't a good idea to put a steel nut max torque spec on an aluminum nut.
You try that max torque and try again thing on a Seekins nut and it isn't going to get you anywhere, except for maybe elongated tool holes which means an out of round nut so you can't install the rail, a split nut, stripped threads, or a cracked receiver. Without at least some shim, the nut bottoms on the receiver.
Shims are used for some aftermarket systems. If someone is selling shims for standard barrel nuts, they are idiots. That is why you have a torque range for standard barrel nuts. If a standard steel barrel nut is bottoming out on the receiver, something is out of spec, and should be exchanged instead of shimmed.