For words that have only 3 letters, there is no 4th letter. For example with the word “add”, there won't be any extra letters Later on and thus needs to be the word "incorporate". The word “addict” is in the BIP39 wordlist however , you might have used “addi” for https://exactlybookmarks.com/story18803885/how-much-you-need-to-expect-you-ll-pay-for-a-good-bip39-definition