I know I had a harrison longbow that was carbon backed that I sold to a guy named larry Burford from Ark,, he said it had fine cracks near the riser and they looked exactly the same so I refunded his money.
bow was 45@28 and 70" and with my 27" draw it eventually delaminated right up the back of the bow..
Jack Harrison told me he was experimenting with carbon on the back but had that happen a few times where it let go right at the grip,, he couldn't help me because I bought the bow used so into the dumpster it went.