Adventureland doesnt have one, either, and it was an opening day land. Also, I'm not sure if the Frontierland plaque features Walt Disney's opening day speech. I believe it is an award plaque or something from some organization honoring Walt Disney for honoring America's past via Frontierland.
I think the only land that has the opnening day words for the land is Tomorrowland, and that plaque was added during the New Tomorrowland of 1998, right?
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The Tomorrowland Plaque was at the entrance to Tomorrowland from 1967 to 1993 (I don't know about one in the earlier TL) The ones, according to Disney, for AL and Fantasyland were OKed by Walt but never instaled! I hope this helps!
"To your left we have a welcome neighbor..... Our GE nuclear powerplant" Carousel of Progress - Progress City