2 entries are registered on port 1501. It is a registered port (1024–49151) — IANA records an assignee, but nothing stops other software from listening here, which is why the number carries more than one entry.
The NetGuard GuardianPro firewall Authentication Client enables secure communication and verification processes between client systems and the GuardianPro firewall on NT4 platforms. Operating mainly over UDP port 1501, it facilitates authentication requests and responses, helping enforce network access control. This service is essential for validating clients before granting protected network access via the GuardianPro security suite.
The registry says what 1501 is registered to. What is listening on it right now is decided by the host, and only the host can be asked. Each of these prints the process behind the socket.
linux
ss -ltnp | grep ':1501\b'
macos
lsof -nP -iTCP:1501 -sTCP:LISTEN
windows
netstat -ano | findstr :1501
On Linux and Windows the process name comes back with the socket; on macOS lsof needs sudo to name a process that isn't yours. Match what it prints against the 2 entries above.
A port number is not a service. Anything may listen on 1501 — what you actually met is decided by the host, not the registry. If a service is missing here, it belongs in the registry.