Adrian. Mike Dalby has a lot of information about "MG" registration numbers issued by University Motors, and if he reads this, no doubt he will respond.
The cars registered around the time of MG 475 were M types and 18/80 Mk2 in April/ May 1930, and so it is unlikely that MG 475 would have originally been on a J2. That does not mean that it could not have been transferred more recently. It is not on the D.V.L.A. website.