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).
Aileen has stayed fairly steady in American naming for generations. All-time it's been given to 44,902 U.S. babies, the 875th most common name by sound today, peaking at 994 in 2011, with 653 in 2025.
By sound, Aileen also includes the spellings Ayleen.