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).
Diane is now well below its former popularity. All-time it's been given to 629,689 U.S. babies, the 2,244th most common name by sound today, peaking at 27,338 in 1955, with 95 in 2025.
By sound, Diane also includes the spellings Dianne, Diann, Dyan. Spellings sometimes heard the same way: Dian.
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).