NVENC - Rate Control Mode


How Rate Control Mode in nvenc works? Will nvenc remove frames, i.e., for example, in case of 100 input frames may there be only 99 frames in output?
Somewhere I read that encoding in nvenc is similar to x264. But x264 rate control may remove frames, and it is bad.

And the second question:
what is the difference between
8 : Two Pass Frame Quality
16 : Two Pass Frame Size Cap
32 : Two Pass VBR