For words that have only 3 letters, there is no 4th letter. Such as with the word “add”, there are no more letters Later on and thus has to be the word "add". The word “addict” is from the BIP39 wordlist however , you might have utilized “addi” for “addict”. https://todaybookmarks.com/story18981883/how-much-you-need-to-expect-you-ll-pay-for-a-good-bip39-seed-phrase-mnemonics-generator