Some older Class A units will not properly display Class B data. The ship will know you are there and have your MMSI, but your name and vessel type will not show on their display.
I have seen this. What I do is run the MMSI number on Google and I get the name of the ship and plug it into the information on the read out. Now when the ship returns the name of the ship is shown immediately. You can also save it in your friends list.