In 1991, a Nintendo Power Magazine had shown one of the only remains left of the prototype of Plants VS Zombies, before PopCap even existed. It was never released on the planned date, the fall of 1991, and was never officially released on the NES as planned. It is said that only 5 cartridges of the game exist however, and only 1 was sold. The person who obtained this cart unfortunately never dumped the game, as they claim it would ruin the value of the game. While there are fanmade ports of the game that were made for the NES, they may not have the prototype structure and code that the original has, but we may never know.
C2A Thanks to The-Mario-Guy on YouTube and TCRF for this information, including the found footage.