While searching for information on the World Peace Flag, I came across this:
"James William van Kirk, a minister from Youngstown, Ohio, designed a peace flag with rainbow stripes, stars and a globe. With this flag, he twice made a peace tour through Europe. The Universal Peace Congress adopted this flag as its World Peace Flag."
The flag in question is this. (An early reproduction of the World Peace Flag. Printed by Koopman, W.A.F., Den Haag). The picture caption mentions that the flag was created in December 31, 1912.
Here's an image of the adopted proposal.
In this provided link there's a 1917 postcard with which the author promoted the flag, and there's even a photograph of the designe with the actual flag, plus additional information on the meaning of the colors, design, etc.
Since this 1912 proposal flag was adopted by the XXth Universal Peace Congress in The Hague as the "World Peace Flag", then we should include it in our own "World Peace Flag".