For words that only have 3 letters, there is no 4th letter. One example is with the word “insert”, there won't be any much more letters Later on and therefore have to be the word "increase". The word “addict” is from the BIP39 wordlist but you might have utilised “addi” https://tbookmark.com/story18876952/bip39-phrase-generator-can-be-fun-for-anyone