For words that have only three letters, there is no 4th letter. For example with the word “add”, there are no much more letters Later on and therefore must be the word "incorporate". The word “addict” is within the BIP39 wordlist however you would've employed “addi” for “addict”. bip39-phrase.com is https://allkindsofsocial.com/story4124211/ledger-seed-phrase-bip39-no-further-a-mystery