Order of display [solved]

If I order by face value and there are two pieces of the same denomination with dates 2000 and 2000-2020, which should appear first? At the moment, it appears that only the first date is taken into account, after which something else is considered, although it isn't clear what, meaning that either order is possible. What does appear to be clear is that the end date is not considered. Does this make sense? To me, a piece only dated 2000 should always come before one dated 2000-2020. I'd also expect a piece dated 2000-2001 to come before one dated 2000-2020, but perhaps that's less clear cut?
The issue was causing a bit of irritation on some Irish notes. The addition of extra dates has resolved it there but it got me wondering what the current system actually is and whether ordering by first date, then last date, then someting else (perhaps catalogue number) would be better?

Hello,
The order was indeed only considering the first date. I changed it, so that the last date is now also considered:

1. 2000
   
2. 2000-2001
   
3. 2000-2020