While an undisputed class, this show indeed did have a number of inconsistencies- the writers just did not pay the attention they should have to the details. It's such a well done show, though (especially seasons 1-4), that they don't detract from enjoying the show.
One of my "favorites": Sophia saying she and Angela are the last remaining of the original family- before Angela morphs into Angelo.
One of the words writer goofs? Having Rose, in a later episode, say her parents' last name was Nylund. D'oh!