"IF EVER I LEAVE THIS WORLD ALIVE"
Lawkeeper Nolan was upset that his foster daughter Irisa would be "sequestered" in the mines "with a bunch of 'slaghead' minders who think she's Typhoid Mary."
"Slag" was the pejorative term used to describe the Tenctonese when the former alien slaves sought refuge on Earth back in the early 1990's (as seen in the TV series 'Alien Nation'.) They were also called "sponge-heads".
'Defiance' takes place in the future of an alternate TV dimension, but it could be that the Tenctonese were to be found on that world as well. And after so many decades, the terms may have been corrupted over Time and then combined to become "slagheads".
Or maybe not. But it wouldn't mean that the Tenctonese never arrived on Earth before the Votan races.
The splainin as to why we haven't seen any Tectonese (no longer "Newcomers" by that point) in Defiance, Missouri, is because most of them settled in the Los Angeles area. That's where their slave ship came down in the desert after the slaves rebelled against their Overseers. And on the whole, they may not have survived the Pale Wars or the radical terra-forming of the planet... especially if they were exposed to massive amounts of salt water during those chaotic times.
But it brings up another question - where are the Tenctonese today in Earth Prime-Time? If they are still around in Los Angeles, shouldn't we have seen at least one in L.A.-based series like 'Major Crimes', 'Franklin & Bash', 'Californication', and 'NCIS: Los Angeles'? (And then there are the sitcoms!)
Splainin? A handful may have decided to remain on Toobworld - the Francisco family, for example, and Cathy Frankel who married to human detective Matthew Sykes. (I like to think that we could see George Sam Francisco on 'Major Crimes' if only Captain Raydor chose to visit his office at police headquarters instead of Russell Taylor's, the Assistant Chief of Operations. I think George Francisco would have been kicked upstairs to a management position based on his prowess in the field.)
But as for the thousands of others? I think they accepted an offer to be taken off-world to a new planet that could be wholly their own, with no indigent sentient species to contend with... and NO salt water! (Lessons learned from the mistakes made regarding Israel and Palestine, perhaps? Except for the salt water part, of course.)
And who would have been able to provide such a monumental taxi service to this New Tencton?
Just sayin', is all.......