If the coating does loosen up, it may just need a longer, possibly a lot longer soaking. With the way it looks I wonder if it was coated or dipped in something early in life and went back into circulation or if it's a past collector's coating for protection that someone has already attempted and failed to remove completely.
I think it definitely circulated with the coating on it based on what I am seeing. I can't imagine it was something applied by a collector as it is very thick in spots. I might just have to try a long soak and see if anything loosens or dissolves off of it.