In Purchase Requests, you see Purchase Ledger Analysis codes, not nominal codes themselves. It is common for this record not to be created when a new nominal code is added. Check that these codes exist.

Your Purchase Requests are likely listing the analysis codes from a view or stored procedure. There will be code in those to determine which codes are returned. Contact support and the team will review these areas and advise on the reasons for exclusion for future reference and system management.