Thanks for the additional information Frank.
Based on your use history, and the amount of ink remaining in your carts, I would recommend emptying the carts and refilling them with fresh ink (but, no need to rinse out the carts- just drain and refill with fresh ink).
Regular agitation of ink carts (always agitate ink bottles before filling/refilling carts), regular use and maintenance (manual cleaning and replacing parts as needed) of the printer, along with proper humidity and temperature in your printing environment will help you get the best quality output, with less issues, and lengthen the life of your printer.
Infrequent use of a printer, paired with infrequent agitation of inks can actually cause flow problems due to thicker ink from the bottom of the carts being drawn into the ink lines, and lead to particle build up in the dampers. This, along with infrequent or no cleaning of internal parts will cause poor ink flow and other headaches. The capping station, wiper blade and flushing box should be cleaned every few weeks (keeping these parts clean will help keep the print head clean and working well), and the bottom of the print head should be cleaned as needed (following our instructions). The dampers and wiper blade should be replaced every 1-3 years.
We are constantly filling ink bottles to keep inventory numbers up, so I'm sure the ink you receive in your new order will be very fresh.
What is the exact message displayed on the printer's LCD screen when the #6, 7 + 8 carts are "being asked to be reset"? Do you reset the cartridge chips, or simply remove and reinsert the carts to get the printer "ready"?
I've never experienced or heard of any cartridge vent hole being too small for the plug to fit, though I usually push down and wiggle slightly to insert the plug into the vent hole (it's supposed to be a snug fit).
I hope this helps, please let me know if you have further questions or there's anything else I can help you with.
Best regards~ Dana