Airbus don't seem to differentiate between one flavour of the A333 family and another.
Just to clarify, the certificated series of the A330-300 are:
A330-301
A330-302
A330-303
A330-321
A330-322
A330-323
A330-341
A330-342
A330-343
Within the A330-343 there are nine sub-models ("variants" in Airbus-speak), identified by 3-digit codes in the range 020 to 057 and MTOWs of either 205, 233 or 235 metric tons (apart from the 057, which is 184 tons).
Re the confusion about the centre tank, none of the A330-300s delivered to date have this, but Airbus announced a couple of years ago that it would be available as an option:
Airbus offers new 242 tonne A330 takeoff-weight capability to extend market coverage *| Airbus Press release