For words that have only three letters, there's no 4th letter. For example with the word “increase”, there are no more letters afterwards and so must be the word "insert". The word “addict” is within the BIP39 wordlist however , you would have used “addi” for “addict”. By next the https://bookmarkswing.com/story20283792/a-review-of-bip39-phrase-list