Hey Paddy,
Very good question! The early Mk1 Barts are a bit different IMO: top end has more bite, a little zingy bur not shrill, mid is a touch clearer more defined, low end identical.
However albeit I've had a few later non USA Mk1's they've been paired with East, Glock, Lakland and Bart pre amps.
The Prose in it's current form has the Aguilar OB2 pre which is known for its pronounced highs, so maybe I'm not making a fair comparison? One observation I can make is I had a 6'er with USA Mk 1's and a Glock pre which was very similar in tone range.
Gaucho