No. 6 by G. Gariboldi in measure 20, is that "G" a G# or a G natural??? Because of the bar line, the rule would be that its a G# (due to key signature), but then why is it remarked in measure 21? I'm not that far along in my music theory studies, but when I asked a teacher of mine who is a composer, he said that either way is possibly correct. I know it's only one note, but I am just curious and unsure. Thanks!

It is a G#. The 19th measure has the G marked natural, and the 21st measure has it marked with a sharp which is not needed. Not sure of the logic, if any.

Thanks.

Those redundant marks usually are just reminders to the player, to avoid possible mistakes by the student

I personally don't mind a reminder here and again. Actually, I end up writing my own courtesy accidentals in myself!

As for the reasoning in this situation, it seems that all of the G-sharps on that entire line are marked (see measures 21, 23, and 25). The only one without a sharp is the one in measure 20. Why is this so? Because it is at the beginning of the line and the key signature is directly to the left. Putting another # in there would make it look like # #, which would be even more confusing.

Why is this so? Because it is at the beginning of the line and the key signature is directly to the left. Putting another # in there would make it look like # #, which would be even more confusing.

Good explanation. Makes sense.