Thanks for the additional information, this is all helpful.
Based on what you say, it sounds possible that this cartridge ran dry and you're dealing with air in the line, though infrequent use can also cause flow related issues such as particle build up in the dampers and/or drying of the print head, etc...
If the VM channel was totally blank, but some nozzles are now printing after a few cleaning cycles, then that's a good sign. When you say "some" VM nozzles are now printing, is that 1-2 individual nozzles, 10-20, 50%, etc? Do more nozzles come back if you do a few more regular cleaning cycles? One initial fill should be enough.
I would not say because you live in Los Angeles that humidity isn't an issue- it's an issue all over the world, and changes thru out the year. For example, here in Vermont the weather channel says humidity is over 80% today, but in our studio it's less than 10% if we don't have the humidifiers running 24/7 (we use about 10 gallons a day, between the two humidifiers we use in our studio). I just checked the humidity for Los Angeles today, and it says 21%, so I certainly recommend you get a hygrometer and monitor the humidity levels in your printing environment. Low humidity combined with infrequent use is even worse for the printer. You can get a decent digital temperature and hygrometer device for about $20.
We include a lot of helpful information in our video and written instructions. These are three places in the cartridge instructions where it says the exit chamber has to be at least 1/2 full for proper flow, and the first line of the refill procedure says "Keep track of the ink level and do not allow cartridges to run dry".
Instructions must be clear and easy to follow, provide lots of helpful information, and be read/followed for the best results. We try to include as much important information as possible, but can not elaborate with all the possible things that could go wrong if you don't do as we advise- then the instruction document would become a book, and fewer people would read them (which unfortunately happens too often as it is). We always welcome feedback from customers regarding our products, as well as the instructions/documents we provide, and certainly want things to be as smooth as possible for our customers.
Have you cleaned the printer's capping station, wiper blade and/or bottom of the print head? If not, you can find there cleaning procedures here: http://www.inkjetmall.com/tech/content.php?133-Printer-Cleaning-and-Preventative-Maintenance
Please let me know your reults, if you have further questions, or there's anything else I can help you with.
Best regard~ Dana