For words that only have 3 letters, there isn't any 4th letter. Such as with the word “insert”, there aren't any much more letters Later on and so needs to be the word "insert". The word “addict” is within the BIP39 wordlist however , you would've made use of “addi” https://bookmarkzap.com/story18720139/examine-this-report-on-bip39-mnemonic-phrase-tool