<p>The official rules are meaningless. Once you’re enrolled in the course (as you are now), you’re obviously allowed to take it and have it count for credit.</p>
<p>Whether you’re ready for it is a different matter that you have to decide for yourself.</p>
<p>fwiw, 31A and 31B are completely different stuff–31A is single-var cal and 31B is a hodgepodge of stuff like convergence tests that you’ll probably never see again in any other course. but yeah, you’ll need to be able to integrate to do 31B.</p>