Search bug: 1980 Belgian 500F not showing when search contains year [solved]

This coin (and the 4 other related types) don't appear when you search for them filtered by denomination and year. https://en.numista.com/catalogue/index.php?e=belgium&st=3&cat=y&ca=3&v=500+Francs&a=1980

Take away the year and they show up. https://en.numista.com/catalogue/index.php?e=belgium&st=3&cat=y&ca=3&v=500+Francs

Not a bug. The Year is ND. The search when 1980 is entered in the Gregorian date works.  https://en.numista.com/catalogue/index.php?e=belgium&r=&st=3&cat=y&im1=&im2=&ru=&ie=&ca=3&no=&v=500+Francs&a=&dg=1980&i=&b=&m=&f=&t=&t2=&w=&mt=&u=&g=&c=&wi=&sw=

The real question is why these are ND and not 1980?

Repost in the Numista coin catalog forum under the tag requesting the modification of a coin in the catalog.

Could be a remnant from the time where coins that had multiple dates depicted on them were most often set as ND (but I thought all of those were fixed years ago).

Idolenz

Could be a remnant from the time where coins that had multiple dates depicted on them were most often set as ND (but I thought all of those were fixed years ago).

Before my time but sounds right. This subject coin started life as a 1980 coin in 2011:

By 2012 it became ND (1980):