I must admit even if all changes are well known, in summary I wasn't aware how much they differ.
According to Henri the recent refit is to improve handling of low speed landing and I guess when they strengthen the rear fuselage eventually they will fit in the hook
A new version of JL-9G made its 1st flight today. The modifications relate to the wing, the vertical tail and the rear fuselage to improve its behavior in low speed flight. This aircraft is used by the Navy to train its on-board pilots.