Let me start by saying that I agree with you about that 100%. I really think that based on what we know and what we can compare it to, we can fairly confidently date it from 1830-34. Which is pretty cool!
The question that I have is this; what would have stopped a maker from making a tang in 1825 that looked like an 1835 tang? Were there actual rules, or how did that work? I think old Judge Lumus knew his razors, but I wonder if he said "I know this one razor by this one maker has this type of tang and is an 1835, so that's the cutoff." or exactly how he did know.