For words that have only 3 letters, there is no 4th letter. Such as with the word “insert”, there won't be any a lot more letters Later on and therefore have to be the word "add". The word “addict” is within the BIP39 wordlist but you would have made use https://bookmarkjourney.com/story18827990/the-2-minute-rule-for-bip39-all-words