Trying to understand Suzanne Bryan’s underarm pickup (3 cast-on edges → 4 stitches?)

Hi everyone, beginner knitter here trying to understand the logic behind Suzanne Bryan’s sleeve pickup method.

In the video, I noticed that in the underarm cast-on section, there seem to be 3 cast-on edge sections/holes, but when she picks up stitches from that area, it looks like she gets 4 stitches out of it.

I’m not talking about the long bars on either side of the underarm. Just the actual cast-on edge section itself.

So am I understanding this correctly: • 3 cast-on edge sections • somehow become 4 picked-up stitches from that same area

And if so, does one of those stitches usually get decreased later? Or do all 4 remain part of the sleeve count?

I think I finally understand what I’m seeing visually, but I’m still confused about the stitch math behind it.