For words that have only three letters, there is not any 4th letter. One example is with the word “increase”, there won't be any far more letters afterwards and thus should be the word "include". The word “addict” is inside the BIP39 wordlist however you would've employed “addi” for “addict”. https://remingtonnjdi433.wordpress.com/2025/01/17/opening-the-world-of-bip39-a-comprehensive-overview-to-mnemonic-expressions-and-word-lists/