Can you use the orb to beat Bowser’s Castle at the end

I'm quite sure it doesn't work

Using an orb to beat Front Door or Back Door counts as seperate (unintended) exits, but does not send you to the credits. I believe this is used in A2 exit, a category extension.

It's worth noting that A2 only appears on the Japanese version iirc. The US version caps it at 96, and I believe the PAL version does too, but I'm not that familiar with it.