Upvote:1
I don't have a complete answer, but since I see dates like 1892 being discussed in the OP links and comments I just want to point out some significantly earlier references.
The 1867 article "Tomtom Beaters, India" on page 431 of Frank Leslie's Pleasant Hours volume III discusses witnessing the "festival of Ganesh Chaturthi" on August 25th 1865 in Bombay.
Also the 1838 The Connexion of the East-India Company's Government with the Superstitious and Idolatrous Customs and Rites of the Natives of India discusses Vinayaka Chaturthi in great detail on pages 88-92
See also the 1841 A memoir of Mrs. Margaret Wilson, in the September 2nd, 1829 entry, writing from Harnai, where it is stated "The annual festival of Ganesha, which is more devoutly celebrated here than in any other part of India..." and there is further discussion in the text and a footnote at page 181.