For words that only have 3 letters, there is not any 4th letter. For instance with the word “insert”, there won't be any a lot more letters afterwards and so must be the word "add". The word “addict” is inside the BIP39 wordlist but you would've made use of “addi” https://socialaffluent.com/story4441435/new-step-by-step-map-for-ledger-seed-phrase-bip39