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).
Sullivan
Sullivan has been climbing in recent years. All-time it's been given to 17,077 U.S. babies, the 631st most common name by sound today, peaking at 1,157 in 2025, with 1,157 in 2025.
Sullivan has no common alternate spellings by sound.
Rising
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).