Okay, maybe I'm too subtle for my own good - the New Kryptonians had space travel before Earth did, plus stealth technology. So they've been in contact with Earth off and on since their first contact in 1996, but nobody remembers it except as tall tales.
Since Kryptonians resemble humans so closely, they probably were able to travel to Earth fairly easily after the Federation was set up, even if they didn't reveal the location of their home planet.
Lara Kal-El will be Clark's daughter, either with Louisa (in which case she looks very good for her age) or her predecessor or even a New Krypton lady while he was between Lois incarnations.
