Something that is not in his possession

Peace and blessings!
The famous dispute between Baal Maor and the Warlocks is whether the stolen item has the power to consecrate the item when the thief does not refuse. The Habanim (28:13) claims that even the Ramban admits that the thief himself can be given the item, because for the thief the item is something in his possession.
It is apparent from these words of the Avnam that he is not in possession, it is not a law of endowment or ownership, but rather of the laws of purchasers. It should be added that it is understood from his words that the disadvantage is not on the part of the acquirer, but on the part of the buyer, who cannot buy an object that ultimately does not reach him, and therefore when the object is already in the possession of the buyer, there is no problem with this.
If I understood the words of the Avnam correctly, it seems that his words should be made more difficult, since the main principle of the law, “He is not in his possession,” is stated in relation to the consecrated object, and even in the case of a consecrated object, all the objects are in his possession, and if so, why is it not possible to consecrate the object?