I received the following reply from the Gardiner, Maine librarian with a copy of August's obituary, which I have sent to Rebecca:
"Well, I have had some success, though not as much as I had hoped. I have found a record of August’s death (18 May 1923) and that he is buried at Oak Grove Cemetery in Gardiner, but, sadly, there is not currently a stone. I am attaching copies of his death notice from the local paper (The Gardiner Journal, 24 May 1923), as well as a record from the annual town report indicating that at his death he was 69 years 2 months and 11 days old when he died. Using a handy online device, I computed his birth date to 7 March 1854. 1854 also aligns with his age in the 1910 Census, though not, as I am sure you know, with the 1920 or 1900 Censuses or with his marriage record. Hard to say what is exactly true, but I do hope this is helpful"
So, we now at least know his death date, and that no gravestone is present. Given the errors survivors often made when an immigrant died years later, and the fact that August listed March 1856 in 1900, it's probably the August born in Fredensborg.When he married Abbie Thornton in 1898, August listed age as 40, and in 1920 census as 63.
At this point in history, it's probably the nearest proof that can be found.