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).
Betty is now well below its former popularity. All-time it's been given to 1,066,302 U.S. babies, the 1,620th most common name by sound today, peaking at 40,163 in 1930, with 222 in 2025.
By sound, Betty also includes the spellings Bettie, Bettye. Spellings sometimes heard the same way: Bette.
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).