Yep Super Dave is correct on the strong/weak tailfeathers on 7/8 varieties, but as to the "B" never seen that on a slab after the grade, are you sure it's on the actual paper in side the holder and not a sticker or written on the outside of the slab? A * or + is common as are some other designations like FBL, FB, FS, Full Bell Lines, Full Bands, Full Steps, etc.
It could be part of a variety designation like a B1 Rev possibly but there should be a VAM
in front of it on a Morgan or Peace dollar
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