Murray, I think calling it G7 when it has a flat seventh is quite logical, as these were the only kind of seventh chords used in early harmony.Early basic harmony was all diatonic (ie using only the notes actually in the scale you were using). The seventh on the dominant was the only one used, and it automatically had a flat seventh(seventh up from the dominant in a major key is always flat). So it was just called a seventh chord, you didnt need to specify that it was flat. Major sevenths came hundreds of years later. the first commonly used chromatic harmonies were dominant sevenths too, being those used in minor keys (eg EG#BD in A minor)