Double entry for Credit memos in AR

Hello colleagues,

I would like to get some details on what GL account codes are hit when a credit memo is created in AR42 and it is applied to an open invoice.I ask this because there is a client who raised credit memos in AR42 and then applied these to open invoices and therafter these memos were released and was followed up by Application closing and distribution closing but there was no effect on 12001 account in GL even if GL190 was also run.The double entry seemed to have not taken place.

Regards

TK