I seem to recall a thread on Indian Diggins before. Yes, I agree, these are strikes of old devices in the early 1930s era of lots of philatelic contrivances, although this one has considerable historic appeal. Obviously they didn't have the appropriate sizes/styles of current year dates for the old devices. I do not know how/why the 1850s device lacks the G, perhaps a later remake?
I use a different method to quickly find the exact date.
From the post office listings on Jim Forte's website:
"Indian Diggings, El Dorado County (1853-1869)",
and without the "G" as
"Indian Diggins, El Dorado County, (1888-1935)"
This narrows the year search for using the uspostalbulletins.com website which has the Postal Bulletin of November 18, 1935 (issue 16825):
"Discontinued ... Indian Diggins ... effective November 30, 1935."
The two websites are at:https://www.postalhistory.com/http://www.uspostalbulletins.com/Home.aspx