Duplicate Appropriation Request

We are having a scenario wherein the user uses a Web Based Capex Form which creates an AR in SAP. So the user has created an AR1 with 4000 Dollar Plan in it. Assigned the AR to the Investment Program Position and then rolled up the Planned Value. Then Budgeted the program in IM32 copying the Plan value. But then AR1 for 4000 Dollar was not sent for Approval. So it sits back in system. Say now they need to Spend 2000 Dollar for which they create another Appropriation Request AR2 with Plan Value 2000 Dollar and which is sent for Approval. Once AR2 is approved Client creates a measure or a project with Plan values 2000 Dollar transferred to the project. Now since the 2000 Dollar spent was a part of the original 4000 Dollar AR1. They manually go back to AR1 and change the Plan value to 2000 Dollar. Is their any way to tie the new AR2 to the old AR1. As at present they do not check in system whether an old AR already exist in system for the same investment type. All I can think of is to monitor before creating AR2 in IMR6 if a similar AR exist for the same criteria (like Investment program ID) Is their any other way for system to check this requirement?