For words that have only three letters, there is absolutely no 4th letter. As an example with the word “incorporate”, there are no extra letters Later on and therefore have to be the word "increase". The word “addict” is during the BIP39 wordlist however, you would have applied “addi” for https://bookmarkindexing.com/story18752236/new-step-by-step-map-for-ledger-seed-phrase-bip39