For words that have only 3 letters, there's no 4th letter. One example is with the word “incorporate”, there are no much more letters Later on and so need to be the word "include". The word “addict” is during the BIP39 wordlist however, you would have utilised “addi” for “addict”. https://nybookmark.com/story20511981/new-step-by-step-map-for-ledger-seed-phrase-bip39