This is so odd. I had a Chesepeake that was almost 16 when she passed. She ate grapes in our yard all of the time, and I had no idea they were harmful. I don't know if she had built up a tolerance to them or not.
I do know that my little poodle doesn't get any people food at all. I just don't take any chances with her, and I wouldn't with my Chesepeake if I had known. The only exception is once in awhile I will give her a tiny little bite of bread. She is getting her teeth cleaned tomorrow and I am just a basketcase tonight worrying about her.