In principle every MFD should see request product information, when any device informs itself on the bus. I have noticed that all devices does not do that. You could try to send product information in every 2 sec with command
NMEA2000.SendProductInformation to see does that make any difference. If it works it may still mean that there is something wrong, but we get a bit more information.
If you have real Actisense NGT-1, that is very strich and request information from all devices.
when try to add the command NMEA2000.SendProductInformation; I have an error "Arduino: 1.8.5 (Windows XP), Board: "Arduino/Genuino Mega or Mega 2560, ATmega2560 (Mega 2560)"
exit status 1
statement cannot resolve address of overloaded function