How Theosophy Came to Australia and New Zealand by Mary K Neff - the copy that my Branch owns is dated 1943. She devotes the first two chapters to "Master Morya writes to Wm H Terry, Melbourne" and "Master Morya writes to Prof. Smith, Sydney."
However, it seems that the first is an addenda in red pencil to a letter from HPB sent to William Terry, which arrived in Melbourne on December 12th 1881.
Being on a letter from HPB, it actually doesn't answer any of the questions above.
The second letter was to Prof. Smith of Sydney - but he appears to have been in India at the time. The numbers given by Mary Neff are 80 and 81.
Chapter 5 of the same book is devoted to a letter that the Professor's wife stitched up in various colours of silk. It turned up back in Sydney with a note from Morya; "Your ladies I see are unbelievers, and they are better needlewomen than our Hindu or Tibetan lasses," OK, so Madame Colomb claimed to have unpicked the silk and then sewn it back up using a hair. Have any of you ever tried to sew using a hair? Given the credibility of said lady, I'd rather believe the Professor.
I also uncovered a reference in private correspondence to Mrs William Draffin of Auckland, New Zealand having had a letter from the masters - but can't verify it.
As for the "New Age" version of the masters - that view needs revising whether or not the original letters were genuine.
I totally agree. HPB is on record as saying she wished she hadn't mentioned the Mahatmas, for exactly that reason. The attention went onto their reality or otherwise instead of actually following their advice. Which is exactly what has happened to Christianity.
For the most part, the Theosophical Mahatmas advice was given to specific people for their specific stage in their spiritual development. In a sense, reading too much and too generally into the letters is really eavesdropping into someone else's spiritual path when we should be concentrating on our own, right here and right now.
How the message is given is immaterial. You never know who is walking in someone else's shoes. For some, yes, they might recieve their next step from reading the letters to Sinnett, especially as his sceptical attitude closely resembles the attitude of many today. For me, however, it was a red rose shoved deep into a hedge in London. And I'm not at all interested in how the rose got there if it gave me a valid message that day.
I can conceive of no scenario by which the handwriting of either of these men could end up in the Mahatma Letters, so the hypothesis doesn't seem worth testing. I did go to Jammu and examine the official indexes of Ranbir Singh's correspondence, which was in several languages but not much in English. Never saw any clue that the Maharaja would write his own letters by hand; the voluminous Jammu/Kashmir correspondence archive appeared to be the legacy of a small army of clerks etc. If Adyar would ever open its archives of correspondence with maharajas, that would be a better possibility-- but it's still a stretch to picture him writing by hand in English. As for Thakar Singh, any correspondence noted in the Dalip Singh Correspondence is in Indian languages with a couple of brief exceptions. Amritsar and Lahore were closed to tourists when I was in India.