SHERLOCK (origin: Gaelic.) From Saor, pronounced as with “h” after the “S,” signifying clear, and loch, a lake, the clear lake.
“Originally, Doyle named his detective Sherrinford Holmes, after Oliver Wendell Holmes – and named Holmes’s sidekick Ormand Sacker. But during the three weeks it took to write the story, Doyle renamed the characters: Sherlock Holmes, after a cricket player he had once played against, and Thomas Watson, after Patrick Watson.” from this site about Doyle.
“Thomas” Watson? “John H. Watson” is the name given at the beginning of A Study in Scarlet, and he was called “James” by his wife in one story, but I’ve never heard “Thomas.”
Maybe Thomas was an earlier name, but the site you listed doesn’t give any more information.
This may be worthless, but I remember a final Jeopardy! question once giving Sherlock Holmes’s original name (or AN original name, anyway) as Sherringford Hope. I’ll always remember that episode, because I nailed the question before they even read it (I just said Holmes’s name as soon as they gave the final category).