Things you thought you knew.
Foods evolve. Claiming a dessert didn’t exist until it had a published recipe to validate it is pretzel logic. In the case of Key lime pie, we have good reasons to believe it started in the late 1800s with sponge fishermen (called “hookers”) pouring sweetened condensed milk on stale Cuban bread in a coffee mug, stirring in a bird egg and topping it with lime juice.
Limes and condensed milk were staples of nutrition at sea, so there was nothing ground-breaking about this creation, and recording the recipe probably didn’t even cross the hookers’ minds. Consider, too, that making a Key lime pie as the fishermen did involved so few ingredients and such a simple process, that it would be the equivalent complexity of making a peanut butter and jelly sandwich today. No fancy recipe required.