All of the following questions refer to the last ancestor born in Poland (hereinafter: the Pole)
This person must have been born to Polish citizens.
If this person lost his citizenship after his child (your ancestor) turned 18, then it doesn´t effect him and the child is still Polish.
On the other hand if you got a positive result for the Pole and his child turned 18 before 1951, you should check again for the child, with the necessary change to the questions.

Pay attention to that when answering. GO?