Every single one is paired with another one square away.
Consider stitches 20, 21, and 22 as a set of 3 which allow for the cable to travel to the right. 20 and 21 would be the 2 stitches of the cable, and 23 would be the purl in the background once the cable is done.
See what I mean?
You'd work through stitch 19, hold stitch 20 to the back, knit the next two and then purl the one from the cable needle.