Rae,
Thank you for your sharp questions.
- I agree that a letter next to an enlarged grouping symbol is not standing alone.
- I believe you are quite right that in the example under GTM 15.3, there is a braille error; namely, in two instances, _| (456, 1256) should be ,_| (6, 456, 1256).
If we can get you more thorough explanation, we will share it here.
–Kyle