I wish I could show you in person. When you actually see and hold them it's not hard to tell. I have a creek where I have found hundreds of pieces over the years. I have gotten to wear I can spot them in a pile of rocks. I will be posting some of my best finds with pictures carved on them over the next few days.
Shell tempered pottery is the youngest, sand and grog (old pottery groung into dust and small chunks) tempered older and fiber tempered is the oldest type of pottery. I would sink the boat if I picked up the shards I see. I do keep large pieces, rim shards or strange patterns.