D7560 misreports ink level

Question

The "Print Quality Report" shows that the Yellow cartridge is empty.  However, I can see through the window that there's still plenty of ink left.
Why is there a disparity between the report and what the state of the cartridge really is?
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Answer 1

Answering my own question.
The printer needed some serious cleaning, especially concerning the ink well area to the right where it does its housekeeping.  This area was so saturated with dried, sticky ink that I doubt the routine maintenance such as moving ink thru the ports to keep them from drying closed was doing anything.  I also cleaned the print head.
On cleaning the ink well - it's not the easiest thing to get in there.  I didn't spend the time figuring out how to remove the outer shell.  There's a small rectangular black plastic well that seems to be there for collecting the ink that gets spent doing its self maintenance.
Two things to look out for with this ink well.
(1) There's a thin spongy filter that sits at the top and is held in place by tension.  Take a pair of tweezers and fish it out.  Wash it and let it dry while you're doing the rest.
(2)  There's a rather fragile frame/collar that lightly snaps against this well from the left.  You can see the hole in the collar piece and the matching notch on the well.  While you're cleaning all the gunk off, this will separate from the well, and I'm pretty sure it's there for the spongy filter.  Treat it gently and replace at the end since the printer probably won't work without it in place.
I cleaned out the ink well with lots of Q-Tips, thin rags, paper towels, and a household cleaner made for cutting thru grease.  What a mess.  But it makes sense that this needs to be done because there's obviously a limit to how much ink can be squirted thru the print heads into this area.  Perhaps HP simply expects its customers to either (a) junk the printer when the ashtrays get full or (b) pay more than the original cost of the printer to have it serviced.  Clearly, HP should design their printers so that this cleaning can be done by the owner.
Also, the print head and the area that contacts with it needed cleaning.  Google this and you'll find some good suggestions on the specific techniques.  The goal is to get all the dried ink cleaned away without damaging the contacts.
Once I had this all cleaned (and you won't get everything without a complete disassembly) and put back together, the printer now doesn't spend tons of time doing its prep before printing.  I surmise that this is because it can do it successfully now that all that globbed up ink has been removed instead of repeatedly trying and failing.
Finally, to solve this specific problem with the Yellow cartridge, I lightly moistened the corner of a rag and pressed it against where the ink comes out.  Because of all the globbed up ink in the well, I imagine the printer wasn't able to keep this cartridge flowing correctly and it dried closed.  Between priming the cartridge with a little moisture and cleaning the printer, all is well now.