Extra alloy

1999 extra alloy? Have someone too?

Is that magnetic?

Yes

Seems like it matches the alloy described in the listing as copper plated steel.

That can happen when the die is used for a long time and gets damaged.  They are call cuds. This illustrates what is happening (I used an 8 rather than the 9) looking at a cross section through the top of the 8.  Normal undamaged die:

The die gets damaged with use and part between the top of the 8 breaks off leaving material in the middle:

It's a fairly common occurrence and doesn't add significantly to the value. 

Ohhh, good eye.  I thought the topic was that the coin was a difference composition.