For words that have only 3 letters, there is no 4th letter. For example with the word “increase”, there isn't any more letters afterwards and thus have to be the word "increase". The word “addict” is from the BIP39 wordlist but you might have made use of “addi” for “addict”. https://bookmarkforce.com/story18919346/the-5-second-trick-for-ledger-seed-phrase-bip39