Oh, dearie me, that was stupid.
I had these 2 lines flopped:
55 token pop /width exch def
56 token pop /height exch def
It all came to me during that last edit where I typed:
For this 215-bit-wide bitmap, I get 27-bytes per row.
And then I looked again at the identify
output. Sure enough, 215 is the height, not the width.