This may be a glib question, but I am curious about this: what happened to pre-Euro-currency-denoted financial instruments when the currency was supplanted by t

This may be a glib question, but I am curious about this: what happened to pre-Euro-currency-denoted financial instruments when the currency was supplanted by the Euro? Did they immediately convert at a defined conversion rate? Did they continue yielding and convert upon interfacing with hard currency? Was there (I assume there wasn't) a biblical jubilee where all debts were reset?