For words that only have 3 letters, there isn't a 4th letter. Such as with the word “add”, there are no more letters Later on and so need to be the word "include". The word “addict” is in the BIP39 wordlist but you might have utilized “addi” for “addict”. One https://rankuppages.com/story4193183/how-much-you-need-to-expect-you-ll-pay-for-a-good-bip39-definition