Here’s my take on this.
In the beginning, you’re working three garter stitches on the sides for the slit in the side with the pattern stitches in between.
Later on, though, after you’ve added a stitch to each side you have 95 stitches on the needles. When you’re finished with the garter edge a few rows up, you’ll have 2 stitches for edge and 93 stitches in the middle.
Unfortunately, the math still doesn’t work out.
I get that you should have 14 stitches to work on each repeat for that first row of the chart, since the 0’s are yo’s. So for later on in the pattern, if you had 96 stitches on the needles, you could have 2 edge stitches and 94 stitches between them–8 pattern repeats.
The bottom line is that I see you’re right about having to cast on 94 from the beginning.
You’ll have to make sure that when the edging is finished that you line up your sections of yo/dec in the pattern to match wherever you started them in the beginning, rather than just follow the chart. Or you can work backwards to see where they would be with the two seam stitches only and work your garter accordingly.