I've now copied my reply to P.M.
The short answer is 'no'. There was a problem a few years ago, which we fixed - since then the only problems have been when trying to fit S-fit accessories to some makes of head that are supposed to be S-fit but which aren't within the manufacturing tolerances of genuine S-fit - so this is a bit of a mystery, which I am sure we can sort out as per my email/PM.