The current ISO standard for JT just has an older version of XT as an informative annex, there is a proposal out for voting to make a newer version a normative

The current ISO standard for JT just has an older version of XT as an informative annex, there is a proposal out for voting to make a newer version a normative (required) part of the standard. Maybe it is intended as a marketing feature "Our exchange file is an ISO standard but the CATIA one is not".