My humble UO-8 seemed to have a French headset, stem and bar. A 22.2 Cinelli stem wouldn't get past the top nut but a Titec stem did. (Yes it's tight but no wobble at all!) Apparently some of this is up to the mercies of quality control in different companies, countries, time periods, etc. BTW: 25.4mm = 1 inch 1mm = .039 .2 mm = .008 (rounded) That makes a .004 cut in wall thickness in the steerer. Seems like this wouldn't bother anything. In the case of the Swiss bikes with French headsets but 22.2 stems; if these are the original pieces then something was altered from standard? Maybe the headset top nuts came oversized?
Pete Geurds
Douglassville, Pa