What is the ruling on disposing of a portion of land that exceeds the agreed-upon amount at the time of purchase, and which has transferred ownership to the buyer without his knowledge and without the seller demanding payment, and is it obligatory to pay the price difference, and if so, at what temporal value should it be calculated?

What you own of the land is what was agreed upon with the seller, unless the seller intended to sell all the registered land, in which case you own all the land. As for the recorded increase, it remains the property of the seller, and you have no right to any part of it except through a new contract. You must ask the seller about the amount he sold you, and do not rely on court registration, as that does not transfer legitimate ownership. And remember the hadith (definition): "Whoever usurps a hand span of land will have it encircled around his neck from seven earths."