As Squall says later on, Jade did not ride for Buxton in 2008. In fact he rode for Redcar before moving to Buxton in 2009 after Redcar decided not to run in the CL/NL. I can't comment on his circumstances at Redcar but I can confirm that he did indeed have the correct visa whilst riding for Buxton.
The only reason why anyone is querying the legality of Mark Jones' visa, and to my knowledge he isn't the only one, is that it has been stated that he only has a 6 month visa. Unless the rules have changed you can only compete in the NL on a youth mobility visa which lasts for 2 years although you can come and go as you please during that time. Something doesn't add up somewhere as there is an obvious discrepancy between the validity periods of the visas in question. Maybe the rules have changed and that explains everything but it would be nice to know either way.