The wiki for open clothes mentions it's usage "implies that nothing is being worn underneath aside from underwear"
However, the open jacket tag, which implies open_clothes, makes no such distinction, and a good portion of its posts are situations where the character has a shirt or similar underneath. In fact, it's probably even the default way of wearing some jackets.
The open coat tag has the same issue: although it mentions the wearer being naked underneath, most of the usage doesn't follow it.
I believe the tag should either be un-implicated, and possibly cleaned up, or alternatively the description of open_clothes should be modified to not include the need of nudity underneath the open clothing.