I knew what the answer was, and thought that "The maximum Tax Rates across all State/Province IDs" described it well. I supopose I should have read more closely and realised that "The maximum Tax Rates per State/Province ID" also described it well, then tried to work out the difference between the two statements. Though I'd probably have picked the wrong one anyway.

Should it have said "The maximum Tax Rate [singular] across all State/Province IDs"?