For words that only have 3 letters, there is no 4th letter. Such as with the word “increase”, there aren't any much more letters afterwards and therefore must be the word "insert". The word “addict” is inside the BIP39 wordlist but you might have applied “addi” for “addict”. Using BIP44 https://webcastlist.com/story20034703/ledger-seed-phrase-bip39-no-further-a-mystery