I agree that the lighter spot on the obv is not an error. It doesn't look like tarnish to me (as that would be darker), but rather something like silver-colored paint or a harshly cleaned patched. I'd say this coin is just worth bullion content now.
"If you climb a good tree, you get a push."
-----Ghanaian proverb
"The danger we all now face is distinguishing between what is authentic and what is performed."
-----King Adz