When the printer stops printing, the amount of ink you were sold as consumable has been exhausted.
There may be "extra" ink left in some cases. This is by design to protect the printhead and maintain quality. You're not paying for the use of this ink, and it being there helps prevent needless charging and cleaning cycles (which would waste ink you did pay for).
DO NOT reset a finished Epson cartridge and reinstall it; there won't be enough ink for the charge cycle, much less the brief cleaning that follows. The printer will not be happy if it thinks the cartridge is full and there's nothing but air left, and you won't be happy when you're out a printhead.
