I think the Phillips patent is 1950s(?) with most showing up early 1960s?
Most vintage stuff (early) is slotted till then. There were other
similar designs like Reed & Prince and Pozidrive which I believe were
work arounds to the original patent. Note European Derailleurs used
slotted adjustment screws while the Japanese used Phillips type.
BOB FREITAS
section 331 row 8 seat 4
SAN FRANCISCO, CA USA