Not sure if this was already mentioned but another reason for having KM# first is if you are trying to sort the display options by reference.
Currently it uses the first reference which is inconsistent on Numista.
For example if you sort 20th Century coins of Lebanon, KM#s are first for some of the coins, but not all.
You end up with a list of KM#s and then a few Lec# while these coins have KM#s as well. But the KM# is not in the first position.
Becomes a pointless sort option if it's not consistent.