For words that have only three letters, there is no 4th letter. Such as with the word “increase”, there are no far more letters afterwards and thus need to be the word "incorporate". The word “addict” is while in the BIP39 wordlist however, you would've made use of “addi” for https://bookmarkfox.com/story4330744/the-basic-principles-of-bip39-passphrase-generator