I have a French 5 franc coin with KM#888a.2 (minted in Africa) made of what appears to be 100% aluminum. The original KM#888a (minted in France) is aluminum-bronze and has an obvious yellowish color. It was my understanding that if the alloy changed, then the KM# would change a whole letter, rather than a decimal (KM#888b instead of KM#888.1 and -.2). What am I missing?