The unlock schedule does not include staking rewards, as they are not ‘unlocked’. They are distributed as specified by network protocol on-chain, and depend on how the total escrow of tokens staked on the network. Because of this, the circulating supply can and will deviate from the token unlock schedule. As you can see on the unlock schedule, it ends right below 8bn tokens. The tokens not accounted for in the unlock schedule are the tokens distributed through staking. 

TLDR; Staking isn’t visualized in the release chart.