Understanding that you want to get it right, if you have the obit that should be enough.
I ordered a marker for my great great uncle based on his obit that said simply who he
had served with. I was able to confirm the service through the web site that Jim Martin
ran, but I did that for me.
I understand that the more you have, the more interesting your subject will be, but I
would go ahead and give it a try at ordering. You may chase that longer than you
want to and still know nothing more. Getting people to change "the list" is sometimes
like trying to rewrite the constitution.
As far as the man's name not showing up, that probably happened more than anyone realizes.
My ggg grandfather died in a Union prison and only showed up in the National Archives and
never "the list" of men.
It may have been that your guy did not actually surrender, or something like that.
Good luck.
Linda