Of course the explanation for 1871 might be something very mundane, such as an enumeration error, and Ann should have been described as servant, rather than ditto for daughter. Her age is out of order for her to have been a daughter. And Robert, as a straw hat manufacturer, might well have had a servant.
And Mary Ann seems pretty confused as to her birthplace - in 1861 as Mary Ann Jakes it was Luton, then Coventry, and in 1881 Thame Oxfordshire!
Can't find Thomas, or Ann, Washington in 1861 though