Don't think older uniglide freehubs were as small as 12t
even Dura Ace freehubs for Race Bikes, in the 80s were 13t top gear cogs

but until the Poster submits pictures It's only going to be a blind guess.

Given Brompton never sold a bike with more than 2 cassette gears.

But people have the ability to make changes, after sale, with home machine shops.