AP_INVOICE_DISTRIBUTIONS_ALL and the PERIOD_NAME

Good day, We have recently upgraded from 11i  to R12 in Oracle EBusiness Suite Accounts Payable.  What I'm trying to determine is: How does the PERIOD_NAME get populated (what drives that entry into the field).

  It appears to be driven by the INVOICE line in the actual application as opposed to the Distributions of the line.   We've got recurring invoices that for some reason are as a majority showing a PERIOD_NAME of APR  but within the Distributions of the line there are dates throughout the year.  In the AP_INVOICE_DISTRIBUTIONS_ALL table the ACCOUNTING_DATE contains the date per the Distribution date within the application.      The invoice number is based on the process for recurring invoices.  SO I'm trying to figure out how does the GL-DATE within the application at the line level get changed and the