Is it important?
I often wonder why nobody questions why Bob Dylan changed his name from Zimmermann - can't remember anybody questioning why - he certainly has never been criticised for doing so, though MacColl was throughout his life in traditional song; he certainly never was when he was prominent in the theatre - maybe it's an inbuilt quirk in the folkie persona!
For many years I was listening to and enjoying the singing of Johnny Handle without realising he was really named John Pandrich - finding this out didn't make one iota of difference to my enjoyment of his singing.
One of MacColl's great critics, who always made a point of mentioning MacColl's name-change was Karl Dallas, despite the fact that he appeared on the scene in the singing duo, Fred and Betty Dallas.
All very silly really
Jim Carroll