It might not need a label

And this is how we end up with the contrast-less useless UIs of today, where it's impossible to tell what's a button, simply some text or a link that acts like a button.. (or a button acting like a link, or a link acting, god forbid, like a link), or what can be scrolled, or was suppose to be able to, or where one window ends and the other begins.

No, be explicit. As explicit as possible, and consistent. If it's nice to have somewhere, it's nice to have everywhere.

The examples provided are excellent, how to understand that the description is missing if there's no label? "Oh, you just have to know, because you've seen this UI before, you live in this UI, right? so you just know!" no, your UI is just one of many I use throughout the day, I don't know where the dates were supposed to be, or that it's broken in this particular case, because there's no hints at what's supposed to be where.