I just got a few sets from S&B as well and they had some black stuff on the high B & E strings as well. They didn't affect the sound though. Not sure what it is, but it didn't bother me or my guitars.
And, yes, I learned my lesson too about cutting them prior to tuning. Due to the round core, this is a no-no with Sunbeams. Tune them, then trim. Otherwise, you risk them going dead.
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