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).
Gustavo
Gustavo has stayed fairly steady in American naming for generations. All-time it's been given to 40,461 U.S. babies, the 1,135th most common name by sound today, peaking at 1,295 in 2000, with 447 in 2025.
Gustavo has no common alternate spellings by sound.
Rising
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).