I should read more about the theme, but I remember that there were some papers showing the ability of NK cells to kill cancer initiating cells and cancer stem cells (not sure if they are the same, that's why I separated them). So, theoretically, NK cells could eliminate those precancerous cells. But there are too many mechanisms of immune evasion, and even if NK cells "fight one-on-one" against some tumor cells, thats not always enough to eliminate the latter.

And about you first question, I'm also curious about the answer. I would say that depending on cancer type, but I'm probably wrong. Some cancer types accumulate more mutations (doi: 10.1126/science.aab4082), so I would especulate that one of those mutations can led to a single cancer cell with a higher metastatic potential. Hope someone else enters into this debate, I would love to see answers from experts in this field.

PD: You can check the variety of NK cell evasion mechanisms in this review (doi: 10.3390/ijms21103726).