I would say he is the same person just because i think the films fit nicer if you believe <PERSON>'s characters are the same person. And regardless of whether the poncho from The Good, The Bad and The Ugly is proof of it linking to A Fist Full of Dollars, there is definitive proof that <PERSON> plays the same character in both A Fist Full of Dollars and For a Few Dollars More.
In For a Few Dollars More There is a part in the film where both the bounty hunters do some research on one another. <PERSON> goes to the funny guy next to the railway and <PERSON> goes to a library or public records office. In <PERSON> scene he browses through a newspaper until he finds an article describing the events of the ending of A Fist Full of Dollars complete with a picture of <PERSON> standing over the dead body of <PERSON>. 295
Now if I'm not mistaken, I can't imagine <PERSON> would go and research someone only to look up an article about someone else.
As for him being known by different names in the movies, I think because no one knows his name they just make one up to call him. I think this can be supported by observing that its usually one person who calls him by such a name and even they don't mention it often. in fact the only time I remember someone else calling him the same name is the undertaker from A Fist Full of Dollars who probably knew to call him that because he has already overheard it from <PERSON> the bartender/hotel owner.
Interestingly because he is the man with no name he could be thought of as <PERSON>. Other variations of this particular name include "<PERSON>", "<PERSON>" and even "<PERSON>...get it?
In For a Few Dollars More he is known as <PERSON> and according to this Wiki link:
http://en.wiktionary.org/wiki/manco
The Italian word for "<PERSON>" is "first-person singular present indicative of mancare" which according to this next Wiki link (sorry about this by the way):
http://en.wiktionary.org/wiki/mancare#Italian
The verb "Mancare" can mean "missing" or "absent". 340