For the other verifications in GSP is as follows:
1. Check Reference: Field status setting is always “Optional” for all GL account group.
2. Check VAT Code: Just apply SAP standard
Default value is from Vendor/Customer
Mandatory check of Tax code by GL account
3. Check Trading Partner: Just apply SAP standard
Basically substituted by Vendor/Customer
Able to enter trading partner manually for accrual posting.