On the DV issue, what they sent you is solid validation. I know there is a lot of info out there about making specific requests in the DV letters. The fact is proper debt validation is very minimal information being provided. There is no requirement to send contracts or affidavits of debt.
You can make any demand you want in a DV or follow up DV. They are not required to provide you with your requests. Personally, I have never heard of a creditor following up with documentation requested from the debtor.
You're somewhat confusing DV with what has to be provided in discovery. In discovery you can ask for your laundry list of items. If the request is for something that is relevant they must provide it. If they don't they can't use the requested items at trial.
It's really a moot point. You're in litigation. There going to have to provide a ton more than they are required to provide in DV to win the case. Disputing at this point is also moot. If you have filed an answer then that is your dispute.
Once you get your discovery request back the courtroom will be where you will dispute what they provided. You will not be sending a dispute letter to the other side.
My personal opinion on account stated is, a large percentage of consumers that have actually answered the lawsuit are the same ones that are aware of the need to have already disputed the bill. Ninety percent of those sued will not answer the lawsuit. The ten percent that do are probably going to be in the fighting mood. They are probably also a little more likely to find creative ways to claim and show the account has been in dispute
Also a JDB or CA can't use an account stated argument. They were not a party to the original contract and are unable to testify if you had an account stated with the O.C. They have no first hand knowledge of what went on with your account prior to the transfer or sale. They have no way of proving an account stated as they do not have all the records from the O.C. and even if they did it would be hearsay. They simply have no way to confirm if the account was in dispute or not.
If you DV a JDB or CA and dispute in that letter then they cannot claim account stated. They can only go back to when they bought the account. If you dispute right off the bat after the dunning letter you have killed what little chance a JDB would have for an account stated claim.