Can you have a pill withdrawal period and be pregnant?

I know that when you're on the pill, the bleeding you have during your placebo week is in fact withdrawal bleeding and not a "true" period, of course, the blood is real, but there is some difference.

Since this is true, is it also correct that if one became pregnant while on the pill, they would not have withdrawal bleeding at all during their placebo week, or it would be very spotty/light? (assuming that no pills were missed). I have heard that this withdrawal bleeding each month, when it is on time, normal, etc. is "proof" that the woman is not pregnant and the pills are working correctly--is this correct?

If you were to become pregnant on birth control pills, a normal withdrawal period would not occur because progesterone production from the corpus luteum gland on the ovary overrides the drop in progesterone from finishing the active pills. Occasionally a woman could have some spotting while pregnant but usually it isn't a full period.