How about a bit more confusion then?
Airbus don't seem to differentiate between one flavour of the A333 family and another. They list only A330-300 orders & deliveries.
A quote from another web site, back in 2008 shows:
"The myth of a centre fuel tank on the A333 persists, but it is false. All A333s have the same fuel capacity of around 98,000 litres vs 139,000 litres on the A332 which has the centre tank".
And another says:
"I fly both the A340-313X and the A330-343X. In our briefing cards in the aircraft log, the letter X means that the cargo hold floors in addition to facilities for handling normal baggage containers, also have additional facilities that are needed to handle dedicated and special cargo containers. We have a MTOW of 275 tonnes (A340) and 233 tonnes (A330) which are standard weights for these versions. Consequently, the X does not mean HGW".
EASA approvals also do not differentiate between the E or X.