Civil War Final service rank

I am trying to determine my 2nd great grandfather's final military rank in the Civil War.

One adjutant report states his final rank as Brevet Captain in April 1863. One of his military service cards looks like it shows a promotion from 2nd to 1st lieutenant - no date given for promotion but does show his final discharge of Feb. 21, 1865.

Question: Am I correct in that "Brevet" means it was a temporary or honorary rank and therefore can NOT be his final rank. Which would mean his final rank was likely 1st Lieutenant??

Question: I have found some of his military cards on Fold 3 but wondering how comprehensive they are or if they'll have the same info as NARA. Is Fold 3 sufficient or should I use NATF 86 to request his military service records from the National Archives?

Thanks in advance!