Disclosure Dispute in the Rules

The Mississippi Rules of Civil Procedure has an interesting issue concerning disclosure of witnesses.  Rule 26(b)(1) provides as follows: 

"(1) In General.  Parties may obtain discovery regarding any matter, not privileged, which is relevant to the issues raised by the claims or defenses of any party.  The discovery may include the existence, description, nature, custody, condition and location of any books, documents, electronic or magnetic data, or other tangible things; and the identity and location of persons (i) having knowledge of any discoverable matter or (ii) who may be called as witnesses at the trial.  It is not ground for objection that the information sought will be inadmissible at the trial if the information sought appears  reasonably calculated to lead to the discovery of admissible evidence."
On the above, some attorneys take the position that the Rules only require the disclosure of names and contact information of witnesses.  Other attorneys, myself included, take the position that you can require the substance of their testimony to be produced also.  The purpose of the Rules is to prevent trial by ambush.  I know several judges who have granted motions to compel on the substance of the testimony of witnesses if it was specifically asked for in discovery. The case that addresses this issue is McKnight v. Jenkins located here.  The Court of Appeals found that the failure fully identify the substance of testimony in discovery was a proper basis to exclude the witness testimony at trial.  I was involved in the case post-trial handling the appeal.  Both arguments were presented and the Court of Appeals went with disclosure being required.