For words that have only three letters, there is not any 4th letter. One example is with the word “insert”, there isn't any more letters Later on and so should be the word "incorporate". The word “addict” is while in the BIP39 wordlist but you would've employed “addi” for “addict”. https://onelifesocial.com/story4179129/new-step-by-step-map-for-ledger-seed-phrase-bip39