[Thus spake Quentin Garnier ("QG: ") 2:02pm...]

QG: What exactly makes you think you want to mount 'sd1b'?

My guess is he's thinking of the old 'fd' driver which makes
different devices of different geometries depending on 'a'..'h',
or something similar

So yeah, what Quentin and a couple others said, paraphrased:

"Disklabel Is Your Friend." [SM]