I've been trying to set some consistent standards for author tag names, e.g. ensuring that we never use just a single name for the tag: thus william-shakespeare instead of shakespeare.
However, to your question about initials versus full first name, I don't think we actually need to be consistent: let's just use whatever name the author is most commonly known by. It seems silly to call a tag john-ronald-reuel-tolkien when not many people know his first names (and in fact he hardly ever used them himself, even among friends). Most authors have a "brand" name, a name by which they're most commonly referred to, and we can use that for the tag name. We can even allow mixtures of initials and full names, e.g. george-r-r-martin.
By all means add other versions of the name as synonyms, but using the author's most commonly used moniker will make the tags and questions more searchable and enable people to find questiona about that author and their works more quickly, which is always a good thing.