[Merry]

I was just thinking that the most usual reason for not marrying was probably that one or other (or both!) party wasn't free to marry. Obviously it could be either of them, but if it was Sarah there might be a chance she would admit to the previous surname on one of her childrens birth certs. I suppose it would be fairly impossible to even consider looking for such a marriage for sarah as there would be so many, but vaguely possible to do so for William Yates (as you have done, but not really found anything). What about looking for Joseph Yates?