The McCracken Research Library has a Miller Single Trigger Co. pamphlet dated 1926
https://mccrackenatcenterofthewest.libraryhost.com/repositories/2/archival_objects/71228

Dan May has an early ad here but it is undated
http://www.millersingletrigger.com/about.html

An ad for the first style top selector Miller, but I don't have the date

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[Linked Image from photos.smugmug.com]