What remedy does a plaintiff have when they receive unverified responses to a request for admission?

In August 2007, defendants served their unverified responses to plaintiffs' requests for admission. Unverified responses to requests for admission are "tantamount to no responses at all." (Appleton v. Superior court (1988) 206 Cal.App.3d 632, 636.) Plaintiffs' remedy was to move for an order that the truth of the matters specified in the requests be deemed admitted. (Code Civ. Proc., 2033.280, subd. (b).) However, plaintiffs failed to file such a motion in a timely manner.