No, NISP won’t provide an ASPSP Directory of the ASPSPs’ productive systems.
In case a PSU-ID allows more than one kind of data item – e.g. IBAN, Name, email address – to identify a PSU, the PSU-ID-Type specifies the type of used data item, hence, whether it’s a name, an IBAN or an email address.
The ASPSP can mandate the usage of a PSU-ID Type. Compare also, IO16.
Note: Also in the case where the ASPSP supports different types of PSU-Ids he might not support the PSU-Id-Type in the requests, since he is able to distinguish between the different typs whithout this explicit information, e.g. he might recognize whether an IBAN or an email adress is entered.
An ASPSP is free to use a proprietary interface. He is obligated to provide the corresponding information and documents to TPPs. This includes in particular a specification of the implemented interface and a testing facility. In case of reasonable doubts that the used interfaces is compliant to the XS2A specification, a TPP can contact the National Competent Authority.
The processes of PSD2 Services as defined in the Implementation Guidelines of the Berlin Group give ASPSPs some degree of freedom when designing their interface. Consequently, Implementer Options describe these APSPS-specific details of the interface’s implementation and PSD2 services.
A brief description on the different implementer option can be found here.
It is the TPP’s responsibility to provide a functionality that is able to handle various versions of the XS2A interface or any other interface used by ASPSPs. ASPSPs are obligated to provide the required information on their interface.