Thanks very much Lindy!
I thought that I should be using the enlarged vertical bar, but the example shown in section 126, example 2 is different from what appears in an augmented matrix.
In an augmented matrix the vertical bar appears inside the matrix itself as a dividing line between two matrices combined into one form.
Another NBA-er found the following: https://www.nationalbraille.org/forums/topic/vertical-line-within-a-matrix/
Is the above-noted forum advice still relevant?
Best,
_don