How to know what will render?

I’m doing something a little funky?
I’ve got a scene with nothing in it at all, and I’m using that to composite.
So my render layers point to the scene/scene(s) and view layers to render.
Really I’m just rendering the main object and the shadow at the moment. And I intend to save those separately, and also save the composite as well.

Why? Well, I want the shadow in it’s entirety, but I wanted separate control for the shadow. I’m going low on samples and rendering with denoise in the compositor. That denoiser seems a lot faster than the render denoise also. But it doesn’t work for the shadow. So I’m adding the shadow to a white image, inverting the result, and pointing that to a combine RGBA where that’s the alpha of black (great way to ensure your shadow is only black when that’s what you’re after)
And I’m doing it that way so that when I render, it doesn’t render every single view layer. Yes, I know you can turn them off, but you have to go do that manually for each one. If you have a lot, that is tedious. Doing it this way Seems like a good idea, when it works. I just can’t figure out what I’m doing wrong, or if I’m stumbled on a bug (unlikely).

It worked once, I thought.
But then I tried rendering a different model set with a couple new view layers that I made after setting it up.

And now the render takes a lot longer, and it’s rendering things it shouldn’t, like the other model sets.

So, is there a way to know what it’s going to send when you hit F12? I’d love to know what it’s actually rendering so I can figure out how to make it Not render things that aren’t needed.

In my “empty” scene, I’ve got the compositor open with Use Nodes checked.
I have 2 render layers. So I would expect it to render something twice.
But it’s also rendering a completely different thing, multiple times and I can’t quite figure out why. And it seems like it renders that Several times.
It shows me the viewer node, but the render result appears incorrect in the blender render window when it’s finished.

Any ideas?