Can an unapplied aamount on a receipt be take to another receipt in R12? If yes then how?

Dear Gurus,

Customer has two invoices and a credit memo.  The customer sends a check and paids in full the invoices and takes the credit but takes MORE credit than the CM was for.  So the AR person short pays the invoices.  Then customer sends a 2nd check and pays for the over credit they took and pays OTHER invoices.  Our AR team was to take the balance on check 2 and apply it to the Receipt 1 and then apply it to the invoices.  They do not want to just pay the outstanding amount on the original invoices on Receipt 2.

Please suggest a way to go. quick help would be highly appreciated