Grav/Anti-Grav and Tech-Level

I always read those TL choices as what COULD be done if you knew the science. So many things are possible at TL8, but without the gravitic theory that is developed at TL9, you can't build it in isolation - as part of an interstellar culture, you can build it at TL8. Same with Jump Drive - in isolation J1 is a TL10 advance, but once you know it can be done, the Jump drive can be built at TL9 - MY OPINION.
Jump drive would be a little more difficult to pin down, since the trope could be that someone found a crashed flying saucer.

And I'm not sure I can pin down the technological level of jump drive factor/zero.