Is there a doubt regarding the lawfulness of the earnings (literally, "in the اجر شبهة") due to an implicit (or indirect) disclosure about previous earnings, knowing that no explicit lie was told, and this resulted in an increase in the new earnings?

If you took the salary based on your information, you deceived him, and the contract is valid, but the employer has the option to uphold it or annul it. You must tell him the truth. If he accepts the salary, it is lawful. If he does not accept it, he has the right to annul the contract, and you are entitled to wages for the previous period commensurate with your work, and you must return the excess. However, if the employer did not rely on your words, then the entire wage is permissible, and there is nothing against you. Deception through lying is forbidden, and renting (ijarah) follows the rulings of selling. Ambiguity (ta'reed) should not be used for deception and taking unlawful wealth.