rsirian1
SCWC doesn't split them but Schön does.
rsirian1
Does Schön explain why they created a new reference code?
Well, that's the problem. Schön doesn't split them, at least not fundamentally.

The Schön reference numbers in our catalog are not correct (at least not in the 2016 edition I have). The both types KM# 491 are also both Schön# 519a (and not Schön# 519 and Schön# 519a as stated in our catalog). Hence the question, why are these two types split?
What Schön does, is making a further distinction within 519a between the dates with material specification P (Schön# 519a.1, with material specification P and mint mark W (Schön# 519a.2) and with mint mark maple leaf (Schön# 519a.3). So if we split P and maple leaf because Schön does, we should also split W to be consistent. Or don't split P, W and meaple leaf at all!
Schön reference numbers versus KM reference numbers:
5 cents copper-nickel: Schön# 519 - KM# 491b
5 cents nickel plated steel with P: Schön# 519a.1 - KM# 491
5 cents nickel plated steel with P and W: Schön# 519a.2 - KM# ?
5 cents nickel plated steel with maple leaf: Schön# 519a.3 - KM# 491
5 cents .925 silver no mint mark: Schön# 519b.1 - KM# 491a (only 2004 is in Krause)
5 cents .925 silver with maple leaf: Schön# 519b.2 - KM# ?
5 cents .999 silver: Schön# 519c - KM# ?
If we split 5 cents nickel plated steel with P and 5 cents nickel plated steel with maple leaf because Schön does, why don't we split 5 cents
.925 silver no mint mark and 5 cents .925 silver with maple leaf? Schön split these exactly the way they split the 5 cents nickel plated steel. The most important characteristics for a catalog are accuracy and consistency. Unfortunately, that's not the case here.