From personal knowledge/experience:
Cell phone companies had subscriber names and addresses for customers. Additionally, a general area could be determined for where the call originated from, based on the cell tower that received the call. This could be wildly inaccurate, as cell signals will travel long distances over water, and/or the distances would vary based on atmospheric conditions, weather, etc. For example, an American close to the Canadian border could be connected to a 911 operator in Canada if the signal was picked up by a tower on the Canadian side of the lake. The 911 telephony system in North America also used triangulation for cell signals, ie: figuring out three towers that the cell signal was received by. That info would generate a general compass bearing for where the cell signal came from, and give a maximum distance as a radius from the main cell tower. Basically, the system figured out a big circle, and the cell signal likely generated from somewhere within it, likely in that compass direction from the tower. In rural or remote areas, with few cell towers, the size of these "big circles" was often large enough that the information was almost useless. There may not even have been three cell towers close enough to pick up the signal from the phone.
And, from a quotable source: https://transition.fcc.gov/pshs/911/Apps%20Wrkshp%202015/911_Help_SMS_WhitePaper0515.pdf
"Locating a mobile phone based on a single cell tower can place the mobile phone in a broad area, but it cannot pinpoint it. As the phone connects to more towers, the accuracy improves. By using cell tower triangulation (3 towers), it is possible to determine a phone location to within an area of about ¾ square mile. In densely populated urban areas, the cell towers are close together, and a much closer estimation of phone location can be made than in a rural area, where the towers are far apart. If the nearest cell tower is busy, the cell signal would be picked up by the next nearest tower which could decrease location accuracy to beyond ¾ square mile or 30 meters of that cell tower.
Sometimes, the diverted signal may go to a cell tower that is out of the PSAP’s jurisdiction."
Note: PSAP = Public Safety Answering Point -- ie: whoever answers the phone when someone dials 911.