I believe Iscore isn't the only factor bank consider for pre-approved offers. My (iscore) is currently 47, and in December, it was even lower at 0. Despite this, I've been receiving pre-approved offers for the past eight months, including the paid tier of the Emerald credit card.
While a Iscore is a good indicator of your creditworthiness, it seems banks might also use other factors in their pre-approval process. It's just like credit score.