§ 2034.620.Expert witness lists or declarations; court authority upon satisfaction of certain conditions

Section 2034.610 opens the motion; this section supplies the substantive test the court has to apply before granting it. Leave to augment or amend an expert witness list or declaration can be granted only if every one of several conditions is satisfied, not merely some of them. The court first has to take into account how much the opposing party has relied on the existing list of expert witnesses in preparing its own case, and it has to determine that granting leave will not prejudice that opposing party in maintaining its action or defense on the merits.

Beyond that reliance-and-prejudice inquiry, the court has to find one of two things about why the change is happening now rather than at the original exchange. Either the moving party, even exercising reasonable diligence, would not have known to call this expert or to offer this different or additional testimony at the time of the original exchange, or the failure to call the expert or offer the testimony back then resulted from mistake, inadvertence, surprise, or excusable neglect, paired with prompt action once the moving party realized the change was needed: seeking leave promptly after deciding to make the change, and promptly serving the proposed new expert information on every other party who has appeared. Even where all of that is shown, leave comes with strings attached. It is conditioned on making the added or changed expert immediately available for a deposition under Article 3, and the court can impose other just terms, letting the opposing party designate its own additional experts or elicit further opinions, continuing the trial, and shifting costs and litigation expenses to the moving party.