For words that have only 3 letters, there is absolutely no 4th letter. Such as with the word “increase”, there aren't any a lot more letters Later on and thus must be the word "incorporate". The word “addict” is inside the BIP39 wordlist but you would've employed “addi” for “addict”. https://maximusbookmarks.com/story19167626/bip39-phrase-generator-can-be-fun-for-anyone