Double Sharps

[MusicArranger]

I’m playing a piano arrangement in B Major which frequently uses this chord: B# dim7. The chord is spelled like this: B# D(#) F(#) An. I don’t understand why the spelling shouldn’t be with a G##. For example, another commonly used chord in this arrangement is B+. This chord is spelled as B D(#) F##. Note: Since I can’t find the proper symbols to display here, I am using the following substitutions: () to show chords which are implied by the key signature. n for natural. ## for double sharps.