Correct, unfortunately many OR's aren't really true OR's that haven't gone through the actual OR school to hear those that administer the ASTB talk about the do's and don't's. The board is making a selection based on what is in front of them, now if you were to retake and get better scores they may just not worry about it, but if you by chance score lower (which has happened) that is a different situation.
I usually tell people with a 7 to give it one shot for SNA before retaking, you do have a chance to see if those getting picked at this board are only 8's and 9's or if it is opening up again.
There are several on here that have done it, just poke around, just because a handful apply for a few few spots doesn't mean it is rare as several things have to line up and be done. No ethical recruiter will tell you to take SNFO if you want to be a SNA because you can just switch later.
Never apply for or accept a designator you won't be happy doing for the next 4-20+ years.