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).
Seth
Seth is now well below its former popularity. All-time it's been given to 166,288 U.S. babies, the 971st most common name by sound today, peaking at 6,725 in 2000, with 505 in 2025.
Seth has no common alternate spellings by sound.
Rising
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).