Did you send this request to the creditor?
Debt validation does not apply to original creditors. It is a debt collection practices process under the FDCPA that only applies to debt collectors, and even then, there is no requirement that a debt collector send any validation.
A DV, if timely, imposes a cease collection bar, and not any requirement to send validation.
Case law has also generally held that debt validation does not require a debt collector to send documentary proof to support a validation, and most of the items you request are not necessary for adequate debt validation, but that is a secondary issue if your request was sent to the original creditor. Your contract agreement and their unchallenged repo of the vehicle consitute documentary validation.
You apparently agree that you were responsible for the loan/debt, so it is unclear as to how you could file a dispute with the CRAs that asserts the debt is not yours.
I do not agree that I am responsible for this debt. The truck was repossessed and sold at auction (I assume). How am I to know what the dollar figure listed on my CR consists of or its accuracy? For all I know, the sale of the truck satisfied the loan and they have mistakenly reported someone else's default on my CR. This isn't a big sophisticated lender but rather a small regional subprime outfit. I have no reason to trust their record keeping which is supported by the fact that they sent me a sales contract for some stranger. While I understand as a co-signer I would be equally responsible for a loan, the reality is it's my brother's debt and he'll resolve it. I am concerned about the black eye on my CR.
State laws govern how a repossed vehicle must be handled as to providing notice to the consumer of the net debt after their disposal of the vehicle. That is not a requirment of the debt validation process under the FDCPA for debt collectors or the FCRA dispute process that documentary proofs be provided to detail the net debt.
I would advise that you contact your state or local governmental agency that regulates handling and notification requirements for repossession of vehicles in your state. They will advise of the applicable statutory or regulatory requirements, and how to proceed if the debt owner has failed to provide required notice of accounting of net debt after disposition of the vehicle.
If you disagree with the debt, then either admin review under your state regs or civil action by filing a suit contesting the debt may provide basis for demanding documentation.