Hi,
as far as I know most of the inkjet cartridges have 2 years shelf life. Although I've never tried an inkjet cartridge older then that, they may work fine. If you are going to install them, let us know if they print fine
I didn't know that a printer can operate both type of inks at the same time. I thought that the printer uses the type of ink which the ink tanks are filled with.
The cartridge's page yield is a relative term. If you print text only pages the yield would be much higher than if you print a text document with a chart (for example) in it. Hope your boss knows that.
I have similar problem with an older deskjet, using the same inkjet cartridges (HP 21 & HP 22). Printed like 10 pages of black doc and everything was perfect. Then the problem appeared - some of the lines ware faded, some were printed only the half (the lower end of all the words in the line...
If you want to survive in the refilling business, you'll have to beat those Chinese manfacturers' prices, which in most cases is almost impossible if you want any profit ;)