The date of the will is a bit odd, but the will is a copy made at probate and there might have been an error in the year (the scribe accidentally putting current year), or the testator didn't know she had died or as this would be the last will made by the testator he might have copied over a lot of text from a previous will without checking if she was still alive. Another possibility. Mary is mentioned with a group of people who all share a part of a bequest. The two people mentioned before her may be deceased as their share goes to their children, maybe the same was intended for Mary (i.e going to her children), but it was omitted either in the original or the probate copy.