updated posting
Mine is #4297, and like yours, has the number on the arc.
I don't remember seeing a Brandis with the number anywhere else, but I'm also not sure we were thinking about it much in the early days of collecting this data. We have 8 Brandis Sextants on the list with numbers lower than 3243: 1146, 1844, 1982, 2734, 2763, 3193, 3227, and 3239. 5 of those have USNO numbers. Interestingly enough, 4 of those have 3 digit vs 4 digit USNO numbers, so perhaps some early Brandis numbers also got early USNO numbers, but not all as we see in the pattern.
Not sure we have imagery of any of them and no notations on where the numbers were located. One is listed as being with the Mariner's Museum, but I can't find it in a quick search of their collection.
My guess is that this one pre-dates the USN purchases during WWI, and never made it into the USNO inventory.
amck