How to read the band →
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).
Henley
Henley has stayed fairly steady in American naming for generations. All-time it's been given to 8,272 U.S. babies, the 1,196th most common name by sound today, peaking at 699 in 2016, with 317 in 2025.
Henley has no common alternate spellings by sound.
Rising
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).