For words that only have 3 letters, there isn't a 4th letter. By way of example with the word “increase”, there won't be any much more letters Later on and thus should be the word "incorporate". The word “addict” is while in the BIP39 wordlist however, you would've used “addi” https://bookmarkforest.com/story18740699/the-2-minute-rule-for-bip39-all-words