limo tip help

I have a party bus 1 way a licoln 1 way and a roundtrip 33 pass shuttle bus . with all 3 the contract includes a 20% tip on each car . should I still tip on top of that ? some people say the limo drivers never see that 20%???

Jess i will ask my dad since he used to own a limo company .....xoxo so excited it is getting so close