Yes, there is quite a difference between the FMS version we model and the later (current) versions. As RNAV and RNP has gained importance, so has the ability to enter "weird" coordinates. As I said, it was possible to do so in our version as well - but you had to create a temporary waypoint (with 5 characters length) to use it in the FMS. Some pilots would enter "HOME" and then the coordinates of their house, just for kicks, for example.
There is also an intricate system to enter straigth (full degrees) coordinates in the way you are trying to do, Ian. But we don´t model that. You can only enter waypoints that are published in the AIRAC. You can check the fix.dat file for available fixes, here is a snippet:
48.000000000 -10.000000000 4810N ENRT EG
48.000000000 -15.000000000 4815N ENRT EG
48.000000000 -20.000000000 4820N ENRT EG
48.000000000 -25.000000000 4825N ENRT EG
48.000000000 -30.000000000 4830N ENRT EG
49.000000000 -9.000000000 4909N ENRT EG
49.000000000 -14.000000000 4914N ENRT EG
49.000000000 -15.000000000 4915N ENRT EG
49.000000000 -20.000000000 4920N ENRT EG
49.000000000 -25.000000000 4925N ENRT EG
Cheers, Jan