This video shows how to make rib increases for either knit or purl first, tbh as it’s a seam, the first stitch will be hidden anyway! As long as you keep the rib columns running correctly from
the new increase stitch (however you make it!!), this is what’s really important
Your rib looks a bit like this:
As long as you keep your V’s or knit sts and your - or purl sts running in columns, the edge sts will disappear in the seam.
Hope this helps and good luck with your project.