For words that only have 3 letters, there isn't any 4th letter. One example is with the word “insert”, there are no a lot more letters Later on and therefore needs to be the word "include". The word “addict” is inside the BIP39 wordlist but you would've applied “addi” for https://bookmarkfly.com/story18828091/how-much-you-need-to-expect-you-ll-pay-for-a-good-bip39-definition