Tenant who broke lease claims there was a typo on lease

[Andrew Robbins]

I bought a multi-family property. One of the tenants I inherited was on an 18-month lease until Sept '18.  He moved out Sept '17.  When I demanded the penalty as stated in lease, he claimed that the lease's end date was a typo -- the end date should have really been Sept '17.  Oddly enough, when I called the agent who set up the lease, the agent confirmed that it was indeed a typo.  Does this mean the tenant is off the hook, or can I still hold the tenant to the terms of the lease?  (I have no reason to believe that the tenant and leasing agent are friends).  It took me two months to find a new tenant, so my real damages are the two months rent (even though the penalty in the lease is for much more).  What am I entitled to, if anything?