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 climbed for decades and has been a steadily popular name ever since. All-time it's been given to 44,902 U.S. babies, the 866th most common name by sound today, peaking at 994 in 2011, with 653 in 2025.
By sound, Aileen also includes the spellings Ayleen.
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).