For words that only have 3 letters, there isn't a 4th letter. For instance with the word “add”, there are no a lot more letters afterwards and so have to be the word "incorporate". The word “addict” is within the BIP39 wordlist however, you might have made use of “addi” https://bookmarkshome.com/story5142078/the-greatest-guide-to-seed-phrase-bip39