I could see this being anywhere from 63-66 having a real tough time. The other variable is it might have got a star from close to PL which would explain the lack of luster? If that's the case I'll guess 66, if it's a lack of luster I'll guess 64
@BigTee44 I was wondering, is that heavy die polish lines by the L in “Liberty” on the obverse, or is that a clash? I kept noticing it and had to ask.
The slab photo shows more luster but nowhere near what you need for a premium gem grade, and apparently not enough for a gem grade. The assigned grade does not surprise me at all.
The luster is definitely lacking, which hurts the grade quite a bit. I'd like to see better pictures of the reverse, as well, because I'm guessing there are some marks hidden in the pictures that we just aren't seeing. The original pictures made it look like a 66 as far as contact marks are concerned. Either way, congrats on the star - that is certainly very attractive toning on that coin!