If any surplus manna turned moldy the day after it was gathered I wonder what state it will be in several thousand years later. Maybe it will have evolved into some kind of life form, capable of blowing itself and its surroundings up.
Exodus 16: 31 The people of Israel called the bread manna. It was white like coriander seed and tasted like wafers made with honey. 32 Moses said, “This is what the Lord has commanded: ‘Take an omer of manna and keep it for the generations to come, so they can see the bread I gave you to eat in the wilderness when I brought you out of Egypt.’” 33 So Moses said to Aaron, “Take a jar and put an omer of manna in it. Then place it before the Lord to be kept for the generations to come.” 34 As the Lord commanded Moses, Aaron put the manna with the tablets of the covenant law, so that it might be preserved.
The text doesn't explicitly state that the intention wasn't for the manna to evolve into something else, to be seen by generations to come. Never underestimate the opportunity to develop a silly theology from Scriptural silence....