I'm with Pat,looks like dry rot to me. Hickory is bad about that if it isn't taken really good care of and out of the weather. Don't look like anything you did. I had several Hickory do that before,thats when I started taking a small piece of the wood I planed to use and do a bend test,if it bends ok
it will usually make a bow.If it has dry rot on the back it will snap just like that did,then I cook with it instead.
Hang in there you will get it done.
Never done many glue up's so don't know about that.I would say that if the core wood is bad it wouldn't matter much what you back it with ,it will break.
Pappy
