It may depend on the timeframe and location, but early census data, land records, wills etc. was collected by people who could read and write - and they often wrote what they 'heard' and spelled it the best they thought.
So if the census taker in 1670 was a native of England he might write down Davis, whereas a native Scot might write down Davies and someone else would write Daviss in another year or if the family moved to a different town.
It is not uncommon, particularly on early records to see this. Here are some examples of how this was spelled in MA prior to 1850:
MATHEU, MATHEU, MATHEWES, MATHEWIS, MATHEWIS, MATHUES, MATHUS, MATHWES, MATTHEWES, MATTHEWS,