For words that only have 3 letters, there isn't any 4th letter. One example is with the word “incorporate”, there are no extra letters afterwards and so have to be the word "increase". The word “addict” is while in the BIP39 wordlist but you might have made use of “addi” https://pr1bookmarks.com/story19018698/the-ultimate-guide-to-bip39-seed-phrase-mnemonics-generator