Wow!
What a catch!
If we go by the Sheldon grading scale I would have to say MS 63 / 64 details cleaned. American companies are generally a LOT more lenient on jubilee crowns that aren't from 1887, especially 1888. There is some softness in the brooch Victoria has but it doesn't seem like wear. The way I've been able to tell apart AU jubilee crowns from MS is if you can see all of St George's knuckles holding the sword and if the horse has a both an eyelid and eye that havent blended together. Also any flatness on the dragons chest / Victoria's veil.
Great score &

.
Worth £110+ any day of the week
My Ms 63 for comparison
