For words that only have 3 letters, there is no 4th letter. One example is with the word “incorporate”, there aren't any far more letters Later on and therefore must be the word "insert". The word “addict” is inside the BIP39 wordlist however you would've utilized “addi” for “addict”. This https://getsocialselling.com/story4250887/new-step-by-step-map-for-ledger-seed-phrase-bip39