Is it the page where you sign if you do not want the horse to go into the food chain? Maybe someone signed it, then a new owner removed it?
A friend of mine bought a lovely coloured gelding at a local sale. Supposedly 4 according to the passport. I called to look at him, and thought he looked like a stallion. Peered underneath, and yes, definitely had extra bits. Vet checked him over, and said he was not yet 3, and it looked like someone had gelded him, but only one ball had been down. He is therefore a rig. But his passport definitely shows him as a gelding.
Hopefully your pony will have no such problem!!