Mistake in the Terminator films and TV series

I was thinking last night about the final ever episode of 'Terminator - The Sarah Connor Chronicles', where in the last 2 or 3 minutes, John Connor and a female T-1000 called Catherine Weaver use a Time Portal to travel forwards in time to the Future War between Humanity and the Terminators.

John notices the remains of the [more or less] dead female Terminator, Cameron, that her remains have not traveled forward in time just as he and the T-1000 both have. He asks "Where's Cameron ? . . . . where's her body ?", and the T-1000 replies "It doesn't go through".

But hang on just a second, in the first episode of the series, when John, Cameron and his mother Sarah travel a few years into the future in the same way of traveling in time as shown in the first 3 Terminator films, only forwards in time rather then heading into the past, Cameron blows off the head of another Terminator called Chromartie, and it's clearly shown that, unknown to the main characters, his head also traveled forward in time with them, despite his Terminator skull's skin covering having been completely been destroyed, so what on Earth prevents his skinless Terminator skull from traveling forwards in time, but stops Cameron's remains from entirely doing so ?.

It's established in 1984's 'The Terminator', that NOTHING metal can travel back in time, not even weaponry like swords or machine guns for example, so if you get a Terminator with no flesh coating to protect it from being disintegrated during time travel, then surely that Terminator would not end up somewhere in the past, it should therefore just get destroyed during it's journey into the past, or even into the future.

Surely therefore it's impossible for the head of Chromartie to travel forward in time when he lost his flesh covering around his Terminator skull ?.

And also, while the T-1000 from 'Terminator 2 - Judgement Day' and the one called Catherine Weaver in the TV series have no flesh covering as well, but they are still made out of metal in liquid form, surely they should not be therefore able to travel back or even forward in time ?.

This would also apply to the T-X from 'Terminator 3 - Rise of the Machines', as she is like a T-101 with a T-1000 exterior - both of which are made from metal and liquid metal !!, so she shouldn't be able to travel back in time either, only Terminators like Arnold Schwarzenegger's with flesh covers, as it's shown in the Terminator universe that anything organic does not get destroyed when time traveling, only clothing and anything made of metal.

Can't believe I did not think about this ages ago.

Well, what do you guys think about that then eh ?

Jason