I don't think that Google accepts +term any longer. They switched several years ago to requiring "term" with quotes. Presumably this was because they wanted to make searches for Google+ names easier. For a while I think they gave a warning, but it seems like they've stopped doing that now.

Edit: Wait, you work for Google, right? Am I the one that's lost? Did they switch back to supporting +term?

Actually, no, I think you're right. I left about 20 months ago, and they disabled support after I left.

Yeah, in my experience the problem is not about Google ignoring search keywords. It is just that their recent updates made it much less apparent that what I'm looking for is not in their index. Their new algorithm seems to drop keywords until it can show me some results that are barely relevant and makes me think that I have to keep tweaking my keywords until I can find what I'm looking for, even if it doesn't exist on the web.

I agree that the lack of a clear "no pages matched your query" is large part of the problem. And as your phrasing indicates, it's also worth distinguishing between "not in their index" and "doesn't exist on the web". Google has a very large corpus, but doesn't include everything.

But the odd part here (and in line with original post) is that there are pages in Google's index that include both terms: https://discussions.apple.com/thread/7169461?start=0&tstart=.... It's just that they don't start until 40 or so results in.

Searching in Verbatim mode without other modifiers seems to create the response that the original post wants: https://www.google.com/search?q=deluge.app+retina&tbs=li:1