In NORW Dr Watson writes in the beginning of the story, ” . . . and I at his request sold my practice and returned to share the old quarters in Baker Street.”
Note, that Dr Watson uses the word “request.” He might have said, invited, asked, suggested, intimated, or any other such word. But, he wrote “request.”
Why would Holmes “request” Watson to return, and why would Holmes arrange to have Watson’s practice purchased and provide the money for the purchase himself?
What is going on here that we have not seen all these years? This is very fertile ground for ploughing.