Does anybody know if there is a difference between 'Buren' of Switzerland and Imperial Buren and Alltrue Buren and also Van Buren - all as a manufacturer of movements? The last items come up for sale in U.S.A. Were they all derivatives for the same manufacturer ? The quality seems the vary considerably.I know 'Buren' was taken over for a time by Williamson of England I believe.I have some of that detail. Thank you.