My can has "Pennzoil" on both the top and bottom in raised letters. It's also opened from the bottom and I don't see anything else inside except a little sludge. I figured mine was pre-50's since the plane on the back is an old twin engine, DC-3 I think, and by the mid-50's the airlines were moving to jets. But that is interesting info regarding the Valvoline cans. I'll remember that for future reference.