Tenant claims he has a lease with different terms

[Edgar Perez]

Good day BP

I recently purchased a 4 unit property in SE Wisconsin ( Kenosha ) prior to closing I asked the previous owner to provide the lease agreements and I tried to get them to submit an estoppel agreement but they wouldn't because it wasn't a "legal" document.  Anyways I did move forward with the purchase and when meeting one of the tenants I had them fill out an estoppel form and on some things they claim do not add up to the lease agreements that were given to me by the previous owner/property manager.  The tenant claims they are on a year lease through May 2018 and that his girlfriend is on the lease with him.  The paper work that I originally received stated that he was on a month to month lease and he was the only occupant of the unit.  My question is if he cannot produce a copy of this lease he claims he has how much responsibility falls on me to track down the documentation of his claimed lease or can I just go with t  he lease that was provided to me at closing?  Any advice and input would be greatly appreciated, thank you.