Time for a distraction.
One of the recent additions to my bibliography of the Inklings in fiction is a semi-novel which has C.S. Lewis referring to Tolkien as "J.R.R." as if that's what he addressed him as.
That reminds me of the question I had when I first began reading the Inklings, which is what they called each other. "Good evening, J.R.R." "How are you doing, C.S."? It sounded unlikely. In those days there were no published biographies of the men to consult for answers. So here's what we subsequently learned.
First, both Lewis and Tolkien were of a generation and class where men customarily addressed and referred to each other by unadorned last names. "Good evening, Tolkien" was not an unlikely thing to have been said.
But when more personal forms of address were used, Lewis was always called "Jack." It was a lifelong nickname he'd borne from childhood. His legal first name was Clive, but I've never encountered him being called that except in school reports.
Tolkien was less of a first-name guy, and his situation is more complex. In the family he was called Ronald, his middle name. In his later years, as personal address became less formal, he tried to get some of his closer friends to call him that, but it didn't really take. Most of the time, if they called him anything other than "Tolkien," it was "Tollers." This was his last name as run through the Oxford student slang process of his youth, which usually took one syllable from the original word and appended -er or -ers.
(One word from this odd slang has leaked out into the general language. For the game association football, the users took soc from association, appended -er, and called it soccer. This name has subsequently dropped out of usage in the UK, where it's just called football, since there's no American football to distinguish it from. But some British speakers still apply the slang process and call it footer, so there you go.)