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).
Asa
Asa has stayed fairly steady in American naming for generations. All-time it's been given to 23,067 U.S. babies, the 832nd most common name by sound today, peaking at 777 in 2022, with 696 in 2025.
Asa has no common alternate spellings by sound.
Rising
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).