There are 5 Defendants in a personal injury lawsuit, and an attorney sends Plaintiff a formal introduction letter explicitly stating that he is only representing 1 of the 5 named Defendants. The attorney then subsequently files an Answer and Counterclaim on behalf of the 1 Defendant, but also concurrently files a Motion to Dismiss for the other 4 Defendants (whom he never claimed to be representing in his introduction letter). Would the attorney not have to had have first filed a Notice of Appearance for the other 4 Defendants before filing a Motion on their behalf since he first disassociated himself as their attorney of record based on his formal introduction letter to Plaintiff? If not, in what instances would a Notice of Appearance need to be filed?
Usually filing a motion to dismiss on behalf of a party would be an initial pleading that would constitute an appearance on behalf of the defendants for whom the motion was filed. But it will depend somewhat on the wording in the motion. If the attorney has been retained by all the defendants to represent them, then the answer is no--the lawyer does not need to file a notice of appearance in addition to filing a motion to dismiss.
This answer does not constitute legal advice. I am admitted in the State of Arizona only. This advice is based on general principles of law that may or may not relate to your specific situation. Facts and laws change and these possible changes will affect the advice provided here. You should not rely on this advice alone, and nothing in these communications creates an attorney-client relationship.