We need to make the distinction between notes which have been demonetized from notes which are still exchangeable but which have had their legal tender status withdrawn. Currently, the single "demonetized" box is being used to indicate both of these entirely distinct concepts. To remedy the situation, can I suggest creating a new box "Legal Tender"? This will require the following options:
Legal Tender
Ceased to be Legal Tender with Date if known
Never Legal Tender
Unknown
The third is required as some banknotes (e.g., those from Scottish and Northern Irish banks) have never been legal tender anywhere. To give an example of why legal tender status needs separating from demonetized, consider a German 100DM note and an Italian 100,000L note, both worth about €50 at the start of 2002. Neither are legal tender any more but the first can still be exchanged for about €50 and so remains an expensive note for a collector to buy whilst the second has been demonetized and can be picked up for a few euros.