My girldfriend gave me this coin yesterday and i found several things that called my attention.

First of all, the date, "several" extra material points isnt it?

And after that i found again different kinds of "extra material":
- Between the heads/hair of Grand Duke Henri and King Albert ( third pic, Red)
- Top hair of Gran Duke Henri (Yellow)
- (In hads is perfectly watchable a full line) Mid hair of Gran Duke Henri (White)
I AM NOT asking if due to all I said, my coin is worth 500€, I just want to learn.
I want to know if all these extra material are common or not, as far as i googled it, i didn't find info but at the same time my girlfriend has at least another coin with the same extra material between the portaits; also I want to know if these can give this coin the status of error coin.
Hoping to get some advices.
Regards.