That is the question. I think it is pretty well accepted Valentino wore a toupee. It was mentioned. Pola Negri, George Ullman, Robert Florey all had their say on the thinning hair issue.
But isn't the issue of Valentino feeling terrified of losing his hair more about male stereotyping? Men were then supposed to have full heads of hair as a sign of virility? When the opposite is true I think.
The subject of that toupee apparently did not die over the years. Just as the slave bracelet, it generated its own lore. From The Honolulu Advertiser, September 18, 1945.
From Simpson's Leader-Times, Kittanning, Pa., August 22, 1960.