Carts can be used until 'empty'.
Problems will occur if you try to do a cleaning and there is not enough ink in the cart, OR the smart card 'counter' has counted down to empty, it can put you in an endless cleaning loop, than can require resetting a parameter in diagnositics mode.
The smart cards contain a chip that identifies the type of ink, the color and an estimate of how much remains in the cart.
The estimate is a count of how many drops have fired and how many pump cycles have occured.
Pump cycles are only an 'estimate' of how much ink is pumped.
Changes in efficiency of the pump, and of the sealing mechanism between the pump and the capping station can account for remaining fluid after the smart card determines 'ink out' or 'ink low' status.
If you have excessive ink left in the cart and it is showing an ink out, contact your dealer for a new smart card to install on the cart.