Do some Red Sphere, Blue Sphere stages have more blue spheres than required?

Solution 1:

You can definitely finish a blue sphere stage with some number of spheres still remaining. I'm pretty sure this is a bug, but I haven't found any definitive sources. I have seen people mentioning this on Twitter before.

I did find this reddit thread where user Domilego4 offers a theory:

I'm guessing the way the game removes one additional blue sphere from the counter when you clear a 3x3 square is that it checks for three things:

• If the four corners have turned red
• If Sonic is within the 3x3 square
• If rings have been spawned at that location

Now, if you watch the video again, you can see that those three conditions are true, so the game removed another blue sphere from the counter.