The reason is in the earlier test they tested it sitting up as a normal car seat
and in the recent one it was tested in the carrycot position.
A VERY safe seat when used like a seat...
caused the crash test dummy seriouse injuries when used as a carrycot. simple as.
Should you choose not to believe the independant tests and the injuries caused to the crash test dummies that is your perrogative... the jane matrix is not the ONLY seat to have been shown to be dangrouse in a crash.
Years back the mothercare daytona was SO dangerouse it was the only thing in the history of the magazine to score 0 In the event of a small crash the babies neck would have snapped and baby would have been dead.
there are LOTS of seats they have found do NOT offer enough protection in a crash... including most (but not the travel tot) mothercare seats, the graco high backed booster, britax highliner, britax ranger, britax trio, all group 1/2/3 car seats (except britax evolva 1/2/3)
The standard for car seats to be tested in is 30mph in a front impact similar to a car driving straight into a brick wall at 30mph which is not representative of many crashes at all.
Which test at faster speeds with different types of impacts so actually see how the crsah test dummies survive in faster crashes mroe realistic of real car crashes, and pesonaly if the dummies are injured in these them thats a good enough reason for me not to use those seats and choose the ones where they dummies are not so hurt.
Car seats that kill children in crashes conform to the BS / EU safety standards so i personally dont trust them at all