For anyone who is interested in understanding how scholars can translate John 1:1c, you must ask them the following. Change the word "logos" by other one, like "Zeus". So, ask them, without talking about of John 1:1, how would they translate the following sentence:
THEOS HN hO ZEUS
All of them will agree that it means "Zeus was a god". But they can admit that it may mean "Zeus was God" if the writer believed that Zeus was the only true God. Both are correct translations, but the context defines the definiteness of indefiniteness of the anarthrous. The problem is if you show them the noun "logos" instead of "Zeus", because it has theological consequences.