Grissom Mercury Helmet

According to the sign in the display case, this is

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Helmet used on Mercury Flight July 21, 1961
Courtesy of Mr. & Mrs. Dennis Grissom

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Now, the Astronaut Hall of Fame claims to have the suit Grissom used on his Mercury flight, and it is displayed with a helmet. I suppose the AHOF sign merely claims that it is the suit which Grissom wore and not the helmet, but it still leaves one wondering.