For words that only have three letters, there is no 4th letter. Such as with the word “incorporate”, there are no much more letters afterwards and thus has to be the word "incorporate". The word “addict” is within the BIP39 wordlist however , you might have utilised “addi” for “addict”. https://www.creativelive.com/student/chris-mccarthy-26?via=accounts-freeform_2