For words that have only three letters, there is no 4th letter. By way of example with the word “include”, there are no much more letters Later on and so has to be the word "increase". The word “addict” is from the BIP39 wordlist however you would've used “addi” for https://tripsbookmarks.com/story18913293/ledger-seed-phrase-bip39-no-further-a-mystery