Richie,
This is from the BL ms which of course Child had a transcript of. If it's in Peter's handwriting then Harvard must have obtained a photo-copy. If it's the original transcription Child commissioned (I forget who did it for him but it's well documented) then it won't be in Peter's hand. The date must be much later, certainly after ABNS was published. Dixon used the ms in his publication for the Percy Society Scottish Ballads so it must predate this, but I'd say c1830-1840. As it comes at the beginning of the ms it may be closer to 1830. I've just had a thought, I haven't got a copy of Dixon's volume, but he might have included Peter's BBA in that.

If you send me a copy I can compare it with Peter's handwriting.