I wasn't sure if this sextant was relevant to your database, but i didn't see it listed while searching the TIGHAR forums and wiki.
I am guessing it was not a calibrated US Navy item, but I'm not sure.
It's the make that we've been investigating but, as you say, not the right kind of number.
We've been studying
pairs of numbers to test the idea that the sextant found on Niku may have been a Navy or ex-Navy sextant.
If a sextant doesn't have an "NO" number on it or on or in the box, then it doesn't help.
Even having more pairs of numbers will never be conclusive, unless we find an existing sextant box with one or the other of the numbers from Niku (
Brandis 3500, NO 1542). That would disqualify the box found on Niku as being part of this series, I suppose.