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Imagine LTE base station roaming or Wi-Fi roaming topologies. In the LTE case, you have multiple ISP base stations that cover different areas in your city. You have a smartphone with an LTE connection up. When your stay at home, you are most likely connected to a single base station (not always but most of the time), which provides the best signal and is, likely, the nearest to you. For example, at home, your phone connects to the base station #5. When you go to work, your phone will roam between the base stations on the way, and once you arrive at your office, your phone will be connected to the base station, for example, #10, because base station #5 will be out of reach and #10 is, now, the nearest tower. Your ISP will always know which tower serves your phone, be it station #5 or #10. They will know the approximate location of your phone based on that and other additional parameters.In the Wi-Fi roaming case, you have multiple access points broadcasting the same SSID. When you go to work and stay at your workstation, you will be, most likely, connected to AP #1. Then, if you go downstairs to visit your coworker on another floor, your phone will roam to AP #2, as AP #1 will be out of reach. The system administrator will, most definitely, have information on which AP your phone useswhen you go to work, your phone roams between different base stations on the way to your office, and when you arrive at any destination, your phone will use (most likely) the nearest tower to you. The ISP knows all the time, which tower/base station your phone connects to. In the Wi-Fi roaming case, when your phone is connected to your office SSID and you move between different floors, you are (most likely) keeping the connection to the same SSID name but roaming between different access points. The system administrator will definitely have information on which access point (AP) your phone connects to.
The same principle can be applied to Bluetooth tag-tracking. Instead of the "LTE base stations" or "Wi-Fi access points", you will have the KNOTs (Bluetooth scanners) and instead of the smartphone that roams between the base stations or access points, you will have the Bluetooth tag that roams between the KNOTs.
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