The changes are a result of better improvement of the translations from the original languages, or new discoveries in the research of the early history of the reconquest of the silent world. You might think that this is a well researched subject, but in fact much of what has been earlier called history and taught in schools has turned out to be myths and fables, especially when it comes to what we know about the six so called "Silent Heroes" and their cat. For example, the claim that Sigrun Storhildur fought off a thousand and one giants all by herself shows up only in a book from year 153, and seems to have no basis in history. However, Emil Hårfagre's good looks and shining hair, as well as Mikkel Mangfare's stoic calm against any danger is attested in contemporary sources, so a lot of the seemingly mythical qualities of these heroes are clearly historical.
;-)