When the white “ASAHI” became black around May 1980 the two little screws near the viewfinder remained as Panheads so this variation became known as the Black Panhead.
The screws were then replaced by the Phillips or star type at some stage to become the Black Phillips. This screw type remained unchanged until the camera ceased production in 1985.
The Panheads in the collection range from 1030697 to 1162300 but the change to Phillips is not consistent as the serial numbers overlap with screw types
The reason why the screws were changed is not known and they don’t play a particularly important role. The overlap of serial numbers is probably due to panheads being replaced by phillips during a repair and most probably the production line used whatever screws were in the pot!