You know what I mean, Harald. Don't make it any harder than what it is.
To make it easy, let's go back to basic genealogical use of sources.
We have primary sources, written at the time of the event. These are mostly the only one that can be trusted 100% allthough we all know of information in these that are wrong to.
Secondary sources are sources written by persons that use primary sources to write their books or trees, where they also write the Sources they have used. These aren't as trustworthy as primary sources, but usually good enough as long as the primary sources they have used are identifiable for each information. Examples are Bygdebok, Familybooks, Historical book and so on.
Tertiary sources are the least reliable ones. These sources doesn't say where they have their information from, they can look like they are written as primary or secondary sources, but lack information about where they have their information from and are written a long time after the events. They can be unsources familytrees found in books or on the web. We should usually not use information from these sources since they can be full of errors, fantasies, fiction and wrongful stories. Sagas will usually fall into this cathegory, since they are unsourced, are written a long time after the events and have parts that obviously or partially are fictional.
Remember, we are after the genealogies, not the histories. If the genealogy is wrong, it doesn't matter how good the story is. The genealogies should be provable to a degree, and if they are only stories or theories they do not belong in a familytree as links between people.
Harald, almost every ethnic Norwegian living today is a descendant of Harald Haarfagre, but there isn't a single person living today that can prove that Harald Haarfagre is one of their ancestors. That is the difference between history and genealogy.
The scientific part comes with the type of sources you have used in your research. If you have used mostly primary sources you have done a good scientific research, if you have used basicly tertiary sources, your research is probably not worth the paper you have printed it on. That is also why most norwegians aren't able to get far into the middle ages in their genealogical research, if they at all are able to get earlier than 1600, the reason being lack of primary sources.