Hard to argue with a factory print!
In Gary's book, he said the non-winged decal was 1951. I wonder if the 1952 association comes from Bill Erickson and his 1952 truck?
Also in Gary's book he shows a copy of a factory ad dated January 1952 with the non winged logo on a bike.
I think I will change my opinion that the non winged logo was 1952 only, as evidence seems to show 1951-1952.