Share 'Enclosed Attic Insulation - Uncover or not?'

I am working on a 1950's colonial with attic insulation consisting of 2"x6" joists filled with loose fill fiberglass. The fiberglass is covered by 1" x 6" decking with 1/4" between the boards. I am recommending adding cellulose to improve the air barrier and insulate. My question is whether I can get away with not removing the old boards, or maybe removing every third one? How much area is needed…