Just my opinion...........I'd take up some of the old floor....If not all of it..........the last plywood cover is "safe"......No Asbestos!..........
I know...The plywood was screwed down real good but bite the bullet and at least remove it........replace with another 1/4" under lay and wait to strip the whole floor later......or get rid of a couple 'easy' layers and cover the floor with underlay/vinyl.................doug