This claim will pay YES coupons if either the French Franc or the German Deutschmark ceases to be legal tender or, while remaining legally acceptable, is substantially replaced in everyday use by the Euro or some other currency, on or before Jan 1, 2003. For purposes of the claim, the status quo on Jan 1, 2003 is the only consideration. The claim cannot be closed before that date, or decided based on events that occur after that date.
"substantially" could mean any of these in one country:
There might be other sensible criteria. But that is what a judge is for.
If the wording is ambiguous, judgement will be based on the perceived intention of the claim.