For words that only have 3 letters, there is no 4th letter. For example with the word “add”, there are no extra letters Later on and thus should be the word "add". The word “addict” is inside the BIP39 wordlist but you would have utilized “addi” for “addict”. To test https://bookmark-nation.com/story18987672/the-2-minute-rule-for-bip39-all-words