Past Production Clause

Dear Forum Members,

Sabine is wanting to lease two acres from our family in an existing unit that has been producing for two years. Our attorney gave us an Addendum that we include in all leases, but it is silent on past production and I want to make sure our family is paid for the production on this two acres over the past two years. It's not much money but we still would like to insure we are paid. Can anyone provide direction on where I might find some language I could add into our addendum. Thank you for your help.