It's very hard for manufacturer testing to catch everything.
Consider this. If Toyota put 5,000,000 miles of internal testing miles on the new Tacoma before releasing it (which is a reasonable estimate).... if they sell 50,000 of them in the first four months (and they did), each one would only have to drive one thousand miles to have the total fleet at 50,000,000 miles, ten times what they would've internally tested.
In the world of cars, it's nearly impossible for internal testing to catch everything. Owners getting hold of them and running them through paces on their own terms is what catches the stuff that slipped through.
They learn through each generation. Hence, they finally fixed a couple major main causes of infamous Toyota frame rust.
If the flaw is bad and frequent enough, if the "Tacoma front top shock hat" issue is common enough, they're gonna emergency fix it by the third model year. Production is a *****, requires redesign, renegotiation with suppliers, sometimes retooling, etc
That said, if one has the money, the LC250 just seems like a better buy than a 6th gen 4Runner. The Car Care Nut underbody review of the LC250 generally shows high quality throughout, and it comes at a cost.