Hi - my name is XXXXX XXXXX I'm a litigation
attorney. Thanks for your question.
The biggest problem that I see with their argument is that in FEDERAL CIVIL LAWSUITS there is a procedure called "initial disclosures". At this time, all parties to the action provide any documents they currently have that are discoverable to the other parties. Thus, if they had discoverable documents and didn't produce them in their initial disclosures, that sounds like an issue.
If they claim that they didn't have these documents at the time and that you didn't ask for them in discovery, then they could have an argument in that limited set of facts. Also, if documents were used as part of a motion that hadn't been previously produced, whether this was proper would depend on whether or not you asked for the documents in discovery and/or whether the documents should have been produced as an initial disclosure.
The best argument may be that the motion contained no exhibits, and that you were deprived of your right to review and analyze these documents before the hearing, which gave you a distinct disadvantage.
Thus, there may be some merit to their claims as outlined above, but if they argued their case and used previously undisclosed exhibits to support the motion and you never received them, that's an issue.