The name I picked was Head of Household. She shows up on Ancestry in the summary books as Miss ...., whereas FindMyPast have her full name.
Again, this is because FindMyPast have also indexed the householders' Census Returns, and Ancestry haven't completed this yet. The reason why the Summary Books often do not contain full names is because enumerators were specifically instructed not to do so. If you look at the examples given to enumerators, you'll see that they have examples "Mr Smith, Mrs Jones, Mr Brown", with no christian names or initials. If you find a Summary Book containing christian names and/or initials, it's because the enumerator did not follow the guidance given in the examples. Also, the Summary Books only contain the names of the heads of households, and no-one else in the household.
I have to say that FindMyPast's transcriptions also leave a lot to be desired. Yesterday I decided to look at the 1911 census for the house that I'm living in, so I typed in the name of the road, and the County - NOTHING. Because this road was once a cattle drove, I subsituted Drove for Road, and the County - NOTHING. In the end I had to type in the name of the town only, and the County, and up came all the roads and streets in the town, including my road, listed as a Drove !