The Validation of Debt Letter is only sent to third party collection firms. Depending on your mix of collectors and your case, UGotiate will recommend which collection firms should be sent a Validation of Debt Letter.
There is no need to send this letter to the Original Creditors. You did not originate the loan or credit card with the third party collection firm that is now attempting to collect on the debt. Remember, the purpose of the Validation of Debt is for a third party collection firm to provide you evidence that the debt exists and that you owe the debt. Because the Original Creditor is who you opened the account with, typically there is no need for them to prove that this debt exist, so there is no need to send a Validation of Debt Letter.