Code of Civil Procedure section 2034.610, subdivision (b), provides the trial court may grant leave to augment a party's expert witness list after the deadline for deposing experts has passed only under "exceptional circumstances." The deadline for completing expert witness depositions is the 15th day before the date initially set for trial. (Code Civ. Proc., 2024.030.) Whether to grant such relief is within the sound discretion of the trial court and its decision will not be overturned on appeal absent an abuse of such discretion. (See Dickison v. Howen (1990) 220 Cal.App.3d 1471, 1476 "the decision to grant relief from the failure to designate an expert witness is addressed to the sound discretion of the trial court and will not be disturbed on appeal absent a showing of manifest abuse of that discretion".)