One card 0 shares the other 50%

Using RaveOS, I've not seen "Shares" have any numbers by them, they always stayed at 0 until today my 470 was showing 50% then 33% while my 480 shows 0. I've mined a total of 70 RVN so I was just curious to what the percentages actually mean if I'm still getting payouts sitting at 0 share percentage?