A lease is a contract. While the contract can be modified or terminated by the mutual agreement of the parties--so if the manager is also your landlord (the person, or at least represents the person or entity, from who you lease), you and he could mutually agree to terminate the lease early--but there must be mutual *agreement* as to the facts.Therefore, a mistake as to the date the lease ends means that there is no real agreement--there can't be agreement when the facts are wrong (especially when you know the correct facts). So an obvious error as to the year the lease ends in this letter would prevent it from acting to modify or terminate the lease.And if the manager is not the one you rent from, and/or does not represent the one you rent from, then his letter has no bearing on your lease.