For words that only have three letters, there isn't any 4th letter. For instance with the word “add”, there won't be any far more letters afterwards and thus should be the word "add". The word “addict” is during the BIP39 wordlist however , you might have made use of “addi” https://bookmarkbooth.com/story19051623/new-step-by-step-map-for-ledger-seed-phrase-bip39