Forgery. Is it possible?

I use Adobesign for certain contracts.  I recently had an situation where a customer signed multiple contracts and is claiming the last one was forged by the sales representative.  The customer lives in a different state than the sales representative and sent us copies of IP addresses for the first few, clearly showing the location was where they live.  On the last contract the IP address on the adobe doc shows the state where the sales representative lives. 

I think the customer changed their IP address with a VPN or something on the last agreement specifically to make the argument that it was forged.

So, my question is, is it even possible for someone to forge an adobesign document?  It would seem to me that they would have to have access to the signer's email address because that is how the contracts are sent, and what shows on the adobesign document as where the contract was sent & who signed it.

Any suggestions or input would be appreciated.