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).
Arturo has stayed fairly steady in American naming for generations. All-time it's been given to 57,291 U.S. babies, the 1,090th most common name by sound today, peaking at 1,093 in 2005, with 446 in 2025.
Arturo has no common alternate spellings by sound.
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).