Thank you, mytwocents

I appreciate your help. I plan to submit documents of my appointment precedure, including approval letter from a higher rank officer, as well as the items you mentioned.
I found another evidence from AAO publication, in which AAO overturned a denial decision based on offer letter made at NSC. Fortunatley, that beneficiary was from the same school as me (my lawyer told me, his case 2 years ago), as well as same title with me.
I will try my best to fight back and let you know the final outcome.