For words that have only 3 letters, there isn't any 4th letter. For instance with the word “increase”, there are no more letters afterwards and therefore must be the word "increase". The word “addict” is in the BIP39 wordlist however , you would have applied “addi” for “addict”. You should https://advicebookmarks.com/story26551524/detailed-notes-on-copyright-wallet-seed-phrase-out-of-bip39