For words that only have three letters, there is absolutely no 4th letter. One example is with the word “incorporate”, there isn't any additional letters afterwards and so should be the word "incorporate". The word “addict” is in the BIP39 wordlist however, you might have used “addi” for “addict”. Art https://onlybookmarkings.com/story18749503/the-ultimate-guide-to-bip39-seed-phrase-mnemonics-generator