I think that's the problem, you have both with and without the N entered in APDL. Our system is designed so that APDL will pull the tail number from the cloud and check to see if it matches any you have entered in APDL already (with or without N). If so, it will use that one already entered, if not, it adds it as it found it online.
So the intended workflow is if you don't have the tail entered already, you edit the one created automatically to match your desired format, and APDL recognizes that and continues using it from that point forward.
In your case with both of them entered, I'm afraid you will have to change each entry with the wrong format to the correct format tail manually to get it back on track.