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).
Bobby is now well below its former popularity. All-time it's been given to 459,326 U.S. babies, the 1,279th most common name by sound today, peaking at 10,786 in 1934, with 412 in 2025.
By sound, Bobby also includes the spellings Bobbie, Bobbi, Bobbye.
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).