Caroline,
Your plant might have been named Popcorn because when the tulip flowered plants came out in the 1960s, the names were changed from the original and here is a list of them: Pandora, Popcorn, Amy, in addition to the original Patrician Andrea and Pink and Red versions that were patented. There was a pale one, and while yours could be the Apple Blossom Rosebud, would check with people who knew the tulip flowered structure to see if you have a very old heirloom.
