Taggs of Bethnal Green and Taggs Island

I am reseaching my paternal grandmother, Charlotte Tagg. She was born at 41 Stepney Causeway, Stepney on 5 September 1877, the daughter of William Tagg and Sarah Ann Fisher. William and Sarah were living in Bethnal Green at the time of their marriage. Family lore is that Charlotte was related to the Taggs of Taggs Island but I cannot find a link. Does anyone have any information about William and Sarah Tagg or Charlotte Tagg? Strangely, they do not appear in the 1881 census.