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).
Leonard was more common in the past and has since settled at a lower, steady level. All-time it's been given to 305,750 U.S. babies, the 1,215th most common name by sound today, peaking at 5,859 in 1921, with 443 in 2025.
By sound, Leonard also includes the spellings Lenard.