As a general rule of thumb, Norse myths are inconsistent at best. There are frequent
inconsistencies with spelling, as well as the chronology of events, and the genealogy of
characters. In some versions of the same myth, Sigemund killed the
dragon Fafnir. In other versions of the same myth, it was Sigemund's son, Sigurd who killed
Fafnir. According to certain texts, Heimdall has nine biological mothers and no father; whereas in other texts, he has a more traditional pair of biological parents of opposite gender.
These inconsistencies arise because there was no one author who wrote the myths, but
rather they are a compilation of myths that were told by spoken word. This can best be
described by the "whisper down the lane" effect.
The greatest difference between Norse myths and Greek myths is that Greek myths are
about winning whereas Norse myths are about losing with honor and dignity. Norse myths
have a much more fatalistic view of the world. Valor is not measured by how well a hero
triumphs over evil, but rather how much he resists evil in the face of adversity.
Norse myths are very cool and are interesting to compare to other myths. However, if you are
looking for consistent, up-beat myths, you should look elsewhere.