It all depends upon HOW the letter is written!
I wonder if my deck service on an US N unrep ship would count? I still have about 240 days not “used” Then all I would need would be regency? of X days and the transfer form? (plus the cargo class $720)
I don’t believe it would count since none of your supervisors had/have a PIC. And it was NOT aboard a USCG inspected petroleum carrying vessel. And besides that any letters you have MUST BE SIGNED by the officer who observed you doing this function. Just your DD-214 don’t cut it… Ain’t interservice rivalry grand!
You are driving yourself crazy over this “used/unused” day crap. Take a breather! You need to carefully re read some of the past posts. The correct info has been given.