Ok, this discussion went on too long internally. Consider the recent Strike Witches posts. I consider bottomless like topless only from the waist down. Others who will remain nameless for now consider SW to be eligible for this tag because the costumes lack leg coverings.

I say post #161930 is bottomless but post #165827 isn't. Feel free to weigh in.

Use panties where panties appear anywhere in the image.

User no_panties when there is a reasonable expectation to be wearing panties but the model is not. (ie no bikini)

Use both in post #161930.

idk whatever~

How about panties whenever shown, bottomless when no panties are worn, and no_pants or something when nothing but the panties are worn?