I'm assuming yon is yarn over? I haven't seen the 'n' before. The vertical stitch is probably the yarn over. Are you ending up with the correct number of stitches at the end of the row? If you are, then you are doing the correct number of yo's and k2tog.
As long as you're putting the yarn in front of your work for the yo, then you're doing it correctly. So if you're getting the right number of st at the end of each row and the pattern is looking like its supposed to, I wouldn't worry about vertical st. Sometimes we just have to blindly follow the directions and see what develops.
Just my opinion, though. :thinking: