Didn't Read All of Kant's Works Before the First Critique?

Kant was a follower of Leibniz before he became Kant in 1781. Before that, prior to the critique of pure reason, he hasn't become Kant yet. He says there are certain things we can't know through reason. And all reason can do basically is show us the limits of our own knowledge. But even someone that really knows con and Hegel, like Adrian Johnston or Slavoy, I don't think have read every all of Kant's works before the first critique.