Thank you to Freki Ingela for this question:
Do you consider Frigg and Freyja to be one and the same great Earth Goddess (eg, Nerthus), or do you consider they are separate deities.
I consider Them to be separate Goddesses, and I do not consider either one a great Earth Goddess, either. They have particular roles in Their families and tribe. While etymologically we may be able to say They were one and the same at some point in the past, either They became two separate Goddesses or They were separate to begin with.
I really have no dog in this race. While it would be interesting to know how the people that worshiped these Goddesses developed their language and understanding of these Goddesses, I worship Them as separate Goddesses. I also consider Nerthus and Jörð separate Goddesses even though both are identified as Mother Earth Goddesses.
While I do believe syncretism has its place, unless I know for sure that a name is a heiti, or that this God or that Goddess actually is x as well as y God/dess, I tend to treat the God, Goddess, Ancestor, or vaettir in question as a separate entity. This approach is more cautious. I would rather find out later that I have been giving a given God or Goddess more offerings than I thought I had than to find out I have been treating two Goddesses as one.