I think the explanation must be that there are two Saunders families that have been combined. There was the merchant family in Banbury, Oxon, and the gentry family in Charlwood, Surrey. The earlier William Saunders were both recorded at about the same time in the early 1450s, one in Banbury and the other in Charlwood. The error seems to go back to the Visitation of Essex, which calls William Saunders "of Surrey" in one line and then "of Banbury" in the next line. I'm not sure how to sort them all out yet, but it seems to me the first step is two separate them into two groups.