On Clark saying he grew up in Kansas, there are 2.8 million people in Kansas. That averages out over 300,000 births a year, probably well over that. Even if they could be sure he had come as an infant, that still would be looking for 1 in 150,000 births. That might give them a head start, but in and of itself would not be enough.
On the other hand, since Lois found him without even having the Kansas lead, it would not be hard for someone else to as well.
