For words that have only 3 letters, there isn't a 4th letter. One example is with the word “include”, there won't be any additional letters Later on and thus must be the word "insert". The word “addict” is in the BIP39 wordlist however you would've applied “addi” for “addict”. The https://userbookmark.com/story18916043/the-5-second-trick-for-ledger-seed-phrase-bip39