The discount is applied to $10/month and is said to make it effectively $8.5 per month, but is actually $8.25 per month, since they claim to charge $99 per year.

Yeah, it's a $20 discount billed annually.

Then that would be $100 per year and none of your numbers for annual plans are accurate. Your website claims $99 per year and claims that is equivalent to $8.50 per month. None of these 3 numbers are equivalent.

You're correct! I made the fix.