Thanks again for your input and it's a good idea. I will be responding to AUSA on those lines. So I understand rule 41 it correctly, it means that if AUSA and plaintiff files the joint dismissal, since there's no court order or response from defendants, or motion for summary judgment, unless the stipulation says "With Prejudice", the case is going to be dismissed Without Prejudice. If the plaintiff files the dismissal by himself or herself, in the circumstances described above, it's still without prejudice.
Bottom line, I or AUSA don't need to explicitly say "Without Prejudice" in the circumstances of my case.
Correct. "Without prejudice" means that the court has not decided which side is right. It does not make any sense to put "with prejudice" in voluntary dismissal requests, I am not sure why some AUSAs are doing that. Even if they put it in, it won't have any effect. But it's our obligation to correct AUSAs if they are wrong, right?