In the answer to question no. 69912 there is a detailed discussion on paying zakaah on shares. Please read it to find out whether you have to pay zakaah on these shares or not.
If you have to pay zakaah and those who are in charge of the shares are paying the zakaah on the shares, then you do not have to pay it again.
If they are not paying it, then you have to pay it for the past years.
See the answer to question no. 69798.
And Allaah knows best.