For words that only have 3 letters, there's no 4th letter. Such as with the word “insert”, there won't be any more letters Later on and so needs to be the word "include". The word “addict” is from the BIP39 wordlist however, you would've applied “addi” for “addict”. Meticulously evaluation https://pageoftoday.com/story4456988/little-known-facts-about-bip39-words