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).
Sergio
Sergio is now well below its former popularity. All-time it's been given to 82,233 U.S. babies, the 799th most common name by sound today, peaking at 2,261 in 1995, with 714 in 2025.
Sergio has no common alternate spellings by sound.
Rising
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).