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).
Wendy was more common in the past and has since settled at a lower, steady level. All-time it's been given to 282,781 U.S. babies, the 1,787th most common name by sound today, peaking at 12,206 in 1970, with 171 in 2025.
By sound, Wendy also includes the spellings Wendi, Windy.