For words that only have 3 letters, there isn't a 4th letter. For instance with the word “increase”, there aren't any a lot more letters afterwards and so has to be the word "include". The word “addict” is from the BIP39 wordlist however, you would have applied “addi” for “addict”. https://socialrator.com/story9906865/bip39-seed-phrase-mnemonics-generator-an-overview