A contract should never be signed by either party without the full terms of the contract written into place. By signing a document with open “fill in the blank” spaces, you leave yourself open to exactly such a situation where the details of the contract are entered after-the-fact.
(In fact, when a person is signing a contract, he or she should ‘strike out’ — i.e. put a line through — any blank spaces left on the document, to discourage changes to the terms after the fact.)
Any debate about the terms of a contract must be resolved in Court if the parties cannot reach an agreement between or among themselves as to the details of those terms. Only a judge can decide what is fair based on the facts of the contract and the terms discussed during negotiations. So if such a situation has already occurred, you must work with the landlord to resolve the issue or be prepared to file suit if a workable resolution cannot be had.
To find balanced lease documents that takes into account the rights of both the landlord and the tenant, see Standard Legal’s Lease Agreements legal forms software.