For words that have only three letters, there is no 4th letter. As an example with the word “add”, there are no extra letters Later on and thus should be the word "add". The word “addict” is within the BIP39 wordlist but you might have utilised “addi” for “addict”. You https://meshbookmarks.com/story19672082/the-ultimate-guide-to-bip39-seed-phrase-github