Yes, there are two other key things that Rafe Zetter tells Alex Ryder:
His father believed he had found
real evidence (italicised in The Dark Wheel novella) for the existence of Raxxla.
He (Jason Ryder) had come back from Deep Space (capitalised in the novella) to get an expedition together.
I take Deep Space to mean 'off the map', hence why it was not in the first game.
There might be something else findable that we need, or which will greatly help us, to locate Raxxla. This could, however, be information at The Dark Wheel base, since if Jason Ryder knew about it and had sent out word that he wanted to put an expedition together, then the information could well have been preserved somewhere and retrieved by other Dark Wheel members after his death.
Oh, and Jason Ryder called his Ophidian shuttle 'Avalonia'