Reconciling the Received Not invoiced account with the GL

RNI is all about timing and how you process. You can start with the PO135 and review the offset accounts (RNI) that are posted to. You should be able to tie the numbers on the report to GL. Keep in mind a few things when looking to tie this out:
1.) Posting of subsystems to GL- After PO135 is run, it pulls a point in time to accrue. After that matching will continue, receiving will continue, if you are posting daily and the current month is not closed in PO and AP then you could have a timing difference in months.
2.) Check to see if in the RNI account if there are other GL/RJ/CA that hit that account. I try to keep just RNI postings from PO in my offset account for ease of recon.
3.) Make sure all journal entries are posted.

Where I have seen the biggest issues in my past was where PO135 was run, PO was closed but AP is left open for a few days at month end to eliminate the need to do so many AP accruals. Matching for invoices recieved in the first few days of the month dated for that month were keyed and RNI was relieved in the current period.

Shoot back other questions and I will try to assist