For words that have only 3 letters, there's no 4th letter. As an example with the word “include”, there are no additional letters afterwards and therefore need to be the word "include". The word “addict” is during the BIP39 wordlist however , you might have applied “addi” for “addict”. In https://sitesrow.com/story8845518/facts-about-bip39-seed-phrase-word-list-revealed