I'll answer: no! The rule are sufficient for understanding what DC is and how to use it, but whether and when to do so openly or in secret has to do with developing your personal style as a DM.
But there’s no guidance on how to develop one’s style. That’s my point.
To me, that's the same as telling DMs whether or not they should role their dice in the open. For the record, I always give the DC in advance unless there's a plot reason why I can't, and the same for rolling dice in the open. But other DMs feel very strongly the other way on one or both counts, and they aren't wrong. For them.
A secondary guide book which explores different options would be fine, and that's kind of what I think the DMG should be. But it shouldn't tell you a right way or a wrong way.
I can’t stress any more how I’m not advocating for one specific right way on all things. I’m advocating for multiple options and an explanation of the pros and cons of each option.
Wait ... we go from "should the DM tell the players the target DC" to ... I don't have an answer?
That wasn’t the question I asked, no. I asked “What do the books tell us about this?” I am not advocating for one approach above any others.
The books offer no guidance. They literally do not describe the process beyond that the DM sets the DC. How the DC is communicated to the players and when? Nothing. It’s remarkable, really.
I do have an answer. It's personal preference. Some people like knowing the exact DC ahead of time, I don't. I feel like it's too gamist. But the thing is there is no one true way and what works for me may not work for another group. I also don't tell people monster's exact HP, or many other numbers although I will tell them the AC after a round or two because it speeds up the game. Again, there's no right or wrong way.
Dude… please stop with the one true way thing. I’m not advocating for one way. I’ll say it once more: I’m not saying there is one correct way.
The text should discuss the different ways and what they mean for the player experience.
Could they discuss it more like the do with The Role of the Dice section in the DMG? Sure. There are dozens of things they could discuss more. How many volumes do you want the DMG to be?
Just one. One that’s useful.
The Role of the Dice section is along the lines of what I’m talking about, except I’d want it to actually say something. I don’t think “some people like A, some like B, and some like both” is really useful without talking about what makes A or B likable, and so on.
I’m suggesting guidance with substance.
How is sound, clear instruction on the implications of various modes of handling the various parts of action resolution not pretty much paramount to any game's text on GMing?
I really don’t understand the resistance to this idea.
I can only come up with two possibilities. The first is that the folks who’ve been playing and DMing longest want the text to continue to cater to them. That it’s okay or even preferable that the books assume prior experience for the reader. I don’t know why anyone would want this, but it seems to possibly be the case.
The second possibility is one I hope isn’t the case, but which I just can’t dismiss. It’s that people DMing just want stuff to be vague and fuzzy so that they don’t have to adhere to any kind of standard of play. They get to do whatever they want without concern how the experience is for the players.