Whenever consulting a genealogical reference work you always need to read the introductory matter for that work in order to understand that work's sources and limitations.
Susan E. Roser's Mayflower quartet (Mayflower Marriages, Mayflower Births & Deaths, 2 Volumes, and Mayflower Deeds & Probates) are all taken from what is known as "The Bowman Files," a collection of over 20,000 pages compiled by George Ernest Bowman, Founder, Secretary, Genealogist and Editor of the Massachusetts Society of Mayflower Descendants, and held by that society. Bowman was the first elite Mayflower scholar and the first to use contemporary records in preference to all other sources. Susan's books are information extracted from the Bowman files and annotated by Susan. Bowman recorded some information that he thought could perhaps be linked to a Mayflower family, but that he either never pursued before his death or that he purused fruitlessly (but not without giving up hope).
In this case it is likely that Bowman thought at one time that Mary Huckens, wife of Samuel Stores, was a Howland descendant, but was not able to prove it.
Dale H. Cook, Member, NEHGS, AGS, MA Soc. of Mayflower Descendants;
Plymouth Co. MA Coordinator for the USGenWeb Project
Administrator of http://plymouthcolony.net