well, I don’t have the sample here, but in the swatch I knit for the technique video on the same needles I knit the sample, I get a gauge count of 20 ridges and 16 sts in the 4" square. So that’s 10 rows (5 ridges) to the inch. Maybe I don’t how to count? Off to check on garter counting videos. I don’t understand looking at your swatches how you are getting 20 rows in 4". I can see that you could be getting 20 ridges, so 40 rows? Is that what you mean?
40 rows, 48 rows, it’s garter stitch which is super elastic row wise. I wouldn’t sweat it, if this is what we’re talking about. The difference between 48 rows in 4 inches and 40 rows in 4 inches is 2 rows – or one ridge – per inch, and could be measured with different results by the same person in the same swatch, since it’s garter stitch. It’s like measuring gauge in ribbing, which is always a fraught result. I remain convinced that you’re good to go.