Radiocarbon dating did not exist at the time of excavation. Radiocarbon dating of objects which have been handled and stored away from their original environment for long periods may not be reliable. In the 1960s an attempt to radiocarbon date some objects yielded a date of 1670 AD.
Radiocarbon dating was not used during the excavation because it wasn't available at the time.  The results of radiocarbon dating on objects that have been handled and stored away from their original environment are unreliable.