For words that have only three letters, there is no 4th letter. Such as with the word “incorporate”, there won't be any a lot more letters afterwards and so have to be the word "add". The word “addict” is from the BIP39 wordlist however you would have applied “addi” for https://socialmediainuk.com/story20190793/facts-about-bip39-seed-phrase-github-revealed