RE: AP voucher posting period
The period to post determines when the expenses appear on the financials - unposted batches aren't reflected in GL totals, posted batches are included. The AP entries can be entered to post in other periods than the current period.
When an AP batch uses a different period to post than the current period, AP totals (Aged AP, Vendor Trial Balance) can differ from the GL control account balances for Cash and AP if the AP batches are unposted.
Period Sensitive versions of these reports are available to help reconcile the GL to the AP ledger, to exclude AP activity not posting to the current period.