For words that have only 3 letters, there isn't a 4th letter. Such as with the word “incorporate”, there aren't any much more letters Later on and thus have to be the word "add". The word “addict” is while in the BIP39 wordlist however you would've used “addi” for “addict”. https://macrobookmarks.com/story19751391/invalid-bip39-phrase-things-to-know-before-you-buy