There are no "other sources" for V'ger. It does not feature outside ST:TMP in canon. STO is not canonical. At all. Any argument based on it is as pointless as an argument based on William Shatner's AU novels. Star Trek canon policy is simple. The TV shows (live action only until recently) and the movies are. Everything else is not. An argument can be made that certain pages of one book that were used on background monitors in ST2 are canonical by virtue of appearing on film, but that's the only thing at all complicated.