C5AE-8505 Water Pump with Dual Casting # (C&D)

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I have a water pump housing that I never scrutinized.  I always saw the casting # as C5AE-8505-D but today noticed what appears to be a double cast letter.  If you look at the letter after the "-" it appears to have both a C and a D cast.   Is this something that happened regularly? 

I tried searching for similar scenarios but did not come up with results.  Apologies if the answer is common knowledge, I am new to ford world.