I see you are new here. Exactly what gloss level black paint was used for the rocker panel and BB rear body panel blackout has been the subject of debate for as long as I can recall. Original cars have been seen with a near flat finish, all percentages of 'semi-gloss' and even a few with a near full-gloss finish. Factory paint charts make no mention of it; sales literature simply refers to it as 'black'.
After decades of spirited discussion, people that worked at the Norwood assembly plant have concluded that it is probably the same black lacquer used for striping. What made it different is it was applied after the body was painted and polished. The blackout areas were not polished; lacquer will dry to a smooth but dull finish. Exactly how dull was dependent on atmospheric conditions. A car painted in January may look different than one painted in June.
So it is up to you. When I had this done, I examined several excellent original paint cars. All were glossy enough to be reflective.
Neither flat nor full-gloss is considered correct.