For words that only have 3 letters, there isn't any 4th letter. By way of example with the word “add”, there isn't any a lot more letters afterwards and therefore needs to be the word "add". The word “addict” is in the BIP39 wordlist however, you might have applied “addi” https://modernbookmarks.com/story18606441/ledger-seed-phrase-bip39-no-further-a-mystery