I was somewhat surprised to learn recently that the USCF used to use a ratings-based "Grandmaster" title, which was a title above "Senior Master". It seems that this was not a lifetime title, and a player would lose it if their rating fell below the rating threshold for that title. In the first USCF rating list which was published in the November 20th, 1950 issue of Chess Life. It lists the different "Classifications" of players by rating, with "Grandmaster" corresponding to a rating of over 2700. This list names two "Grandmasters" - Reuben Fine, and Sammy Reshevsky (though Reshevsky was listed as "Inactive"). In looking at a 1955 USCF rating list, I see that the only name listed on the rating list as a "Grandmaster" was Sammy Reshevsky. If I look at a 1958 rating list, the threshold for Grandmaster was dropped to 2600, and there were now once again two USCF Grandmasters - Sammy Reshevsky, and Bobby Fischer. The situation was the same in 1960, with the same thresholds and the same two names as the only "Grandmasters". Then, in the June 1961 issue of Chess Life, there was an article by Arpad Elo describing the mathematics of the USCF rating system (I'm presuming this was about the time of the transition between the old Harkness rating system, and Elo's new system), and the highest title it listed was the "Senior Master" title, for players with USCF ratings of 2400 and above, and it mentioned that "Grandmaster" was now a sub-category of "Senior Master" used to differentiate players rated over 2500. (The article also mentioned that, as originally designed, the rating system was meant to be calibrated such that a rating of 2000 corresponded to a level of ability to achieve a 50% score in the US Open, which I thought was very interesting...) In the 1961 rating list, Reshevsky and Fischer were both now listed as "Senior Masters". And that was apparently the end of the USCF "Grandmaster" title.
What was the reasoning for this change? Were there any other players besides Fine, Reshevsky, and Fischer who ever had the USCF "Grandmaster" title? They were the only ones I found.