Or maybe i am overthinking it?
A key thing I forgot to mention, Sir herlig9, is "Mr." in
Tolkien's context does not mean "Mister" as we understand it today.
Tolkien was drawing on his Edwardian/Victorian background.
Mr. was the shortening of the word "Master." There is a history to how "Master" transitioned to "Mister" as well, if you would be interested. But it is an etymological thing, with "master" preceding "mister" in the forward motion of the roots.
So we are to understand
Sam is not saying "Mister
Frodo". He's saying "Master Frodo."
However, this could also be dependent.
There was a period of time in its transition, when "Master" was applied mostly to the younger
men of 'greater position or status' so to speak, while "Mister" was reserved for the more aged among the male population. (you can see "Mister" was gaining ascendancy as the 'most respected title.' We can all recall movies etc. where we hear the term "young Master" being applied.... again, early in the transitional period before distinctions were more clarified.)
Given the period Tolkien is drawing IN HIS TEXT for the earlier
ages of
Middle-earth, I am (personally) feeling his intent was for Mr. to mean "master Frodo" - both due to the earlier age, before Mr. was "mister", and because of the Boss/Employee relationship of Frodo/Sam as well as their close familiarity.
So Ent construes it all at present, absent other information not yet found.
(I'm not sure I've seen this question covered in any other readings to date, or Tolkien speaking to it directly. When I have access to all my digital
materials, i'll dig it deeper.)
That said, the shortening to Mr.
did start to occur when "Master" was the only use. It followed through the transition, applied to both "Master" and "Mister." A wholly clear-cut thing of course, crystal clear to the most unastute observer. (NOT..!!)
Word transitions are difficult things, leaving much rubble in their wake ofttimes.