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).
Serenity
Serenity is now well below its former popularity. All-time it's been given to 77,625 U.S. babies, the 302nd most common name by sound today, peaking at 4,481 in 2013, with 2,209 in 2025.
Serenity has no common alternate spellings by sound.
Rising
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).