Following surnames isn't always easy. There are plenty of ways our ancestors could trip us up. Spellings were very variable even quite late on. A simple name like Smith could be written as Smyth or Smythe. Unfamiliar foreign names have always been particularly difficult, especially when you don't share the same alphabet.
Inconveniently for us, our ancestor changed their names. Sometimes the reasons are obvious. Foreign names may be changed for safety, economic or cultural reasons. Sometimes the reasons for the name changes are a mystery. Up to the seveteenth century aliases were quite common in England but why is not certain. I don't think they were all convicts escaping from the law so the reason for adopting them may be lost in the mists of time. I saw one the other day which was a Haynes alias Hinde. Both names were given at the time of burial in sixteenth century Culmington in Shropshire. In the few minutes I was doing the research there were another two aliases I found:
Charles Corne alias Cooper Culmington parish register buried 1638
Thomas ap Evan alias Looker burial 1633
There seems to be no rhyme nor reason to it at all. Was Thomas ap Evan a good looker or what?
Later, Registrars, vicars and census enumerators have a good go at changing the surname which they found hard to make into something familiar. Goodall became Goodwill or Goodell, Kirkland became Kertland. William Powell was baptised as William Poley and only became Powell on his marriage. Did the registrar write the name down incorrectly?
Names in the the fourteenth century were certainly simpler - they often told you not who it was you were talking about but where they lived as well. http://www.sharehistory.org/janes/uploads/7015-worfield-estreats-1309