Solid line = floor (spellings that unambiguously belong to the group). Shaded band up to the dashed edge = ceiling (the most it could reach if every ambiguous spelling counted here).
Quincy has stayed fairly steady in American naming for generations. All-time it's been given to 35,920 U.S. babies, the 838th most common name by sound today, at an all-time high of 818 in 2025.
By sound, Quincy also includes the spellings Quincey.