For words that only have 3 letters, there isn't a 4th letter. For example with the word “insert”, there won't be any extra letters afterwards and thus has to be the word "incorporate". The word “addict” is within the BIP39 wordlist but you would have made use of “addi” for https://myfirstbookmark.com/story18848655/not-known-facts-about-bip39-english-words