The answers to the questions are pretty simple. There are 3 kinds of subpoenas. One is that you have to produce records, usually instead of having someone appear. The second one is that you have to appear in person and testify and the third requires both.
One of the saddest parts is that you don’t even have to be involved in a criminal or civil case to get served with one. If you have in your possession or it seems you might have records or information that are needed or wanted you are subject to getting a subpoena.
The request for records can be just about anything. Now some places on the web will tell you that some things are not covered by subpoenas. That is not entirely correct as anything can be required to be produced. It may require a little more detail and work but almost nothing is beyond the reach of a civil subpoena. The criminal subpoenas can reach anything. I hope that help you to understand that the records only have to be remotely and likely to contain information relevant to the case for you to have to produce them.
Depending on your location and the local court rules you can get information about being sued prior to being served if you are not in the same location. The paperwork can take a few days, weeks or months to get to people if the address is not known or a ways from the court. The docket number can be used to find out the information. Now some seem to think that being out of state protects them. Well in the US it did for but not any longer. The Uniform Code was amended in 2007 to allow a court to have a court in the other state order the person to honor the subpoena issued in another state. Living out of state is no longer a hiding place. The rules for each state and the procedure are different but the concept is the same.
The Federal Rules of Evidence covers the federal issues like copyrights and has procedures for handling subpoenas for both civil and criminal cases. Criminal cases are not an issue as they simply issue an arrest warrant which is honored in every state and territory. A warrant does not mean you are guilty it just means the evidence is compelling enough to have you picked up for questioning or to be held for a hearing.
Now you know that the cases can be handled even if the litigants are out of state. You also now know if you have the possibility of being sued you can get a heads up if you have some information.
Disclaimer: I am not an attorney. These are my personal opinions and general information only. These are not legal advice and should not be used as such.