With the Shelley upgrade, Cardano became a fully decentralized and dynamic ecosystem. In the Byron era there were no stake pools (and therefore no staking) and the blockchain was run by the creators alone.
You're missing the prefix, i.e. e1 in this case.
const stakeAddressDecoded = 'e1'+addressDecoded.substr(addressDecoded.length - 56);
You have to add e1 (or e0 in case of testnet) as prefix.
Check page 113-114 for more details on prefix specifications: https://hydra.iohk.io/build/7918420/download/1/ledger-spec.pdf