[Tetlee]

Just to answer my own question in case it's useful to anyone else.

The free gold one month trials are clearly linked to the actual console and not linked with the hard drive. I have my old 20gb hard drive attatched to my new console and having just set up a Japan account in the hope of downloading the Resi5 demo(which is now region-locked by the way) I can confirm that the new Japan account has been given the gold trial(and I'd already used up my four free trials on my old 360 which this hard drive belonged to).