We pushed out a change today that should allow you to retrieve the customer ID of unlinked accounts from the InfoService. If you call the InfoService using the ApiUsageType of UNIT_COUNT_FOR_CLIENTS while authenticated as the unlinked non-MCC account, you should receive back a single entry in the response with the email and customer ID of the authenticated account. It's not necessary to populate the clientEmails or clientCustomerIds fields of the selector. Calling the InfoService authenticated as an MCC account will behave the same as before (one entry for each client account). Let me know if you have any questions.