Sorry I was busy that day and didn't get to finish my comment.

If its shiny on the inside what would cause it to be dull on the outside. A cardboard box does not protect it from all the elements were as the inside is encased in metal providing more protection for the original plating. If you can find one of the factory replacement motors with the part number sticker on it remove it and its most likely shiny. So far I have not been able to find anybody with a pic of an "in the day" wiper motor. So with out documentation from the past it is very hard to judge exactly what is correct. As far as the numbers I have cores with very light stampings date codes 0111 and 2220 are usually very light. There are many variances to this and ultimately its up the individuals choice.