Yes. The mediaeval system did use the 7th tone but named it in a round about way.
Note seven of the ut/do (C) hexachord was arrived at in two ways:
1) 4th tone of the fa (F) hexachord (B flat)
2) 3rd tone of the sol (G) hexachord (B natural).
The tone existed, but was named as 4 of 4 (B flat of F) or 3 of 5 (B natural of G).
If I remember correctly, this is from where the flat, natural and sharp signs derive. They are all based on the letter b.
Sure, if you say so. This is way over my head, I do audio engineering, not music. I can tell you if a tone is 500Hz or 1k or 10k, but if you asked what B flat was, I would guess a bra size :p