You're correct assuming our number is correct. I looked around and now I think it's right, although it seems really high.
It seems very high. Given those numbers, 1.053, and assuming it would finish at or near the cream ale 1.013 +/- it would add 5-6% to the original ABV?
My hydrometer after adding the blackberries only reads 1.018, not sure how accurate this would be given the sample is only the liquid, none of the solids from the puree. If this was accurate, and it were to finish at the original 1.013 it would be about .66% alcohol added to the original 6% Of the base cream ale, correct?