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).
Julie was more common in the past and has since settled at a lower, steady level. All-time it's been given to 521,916 U.S. babies, the 1,256th most common name by sound today, peaking at 18,611 in 1958, with 323 in 2025.
By sound, Julie also includes the spellings Juli, Julee.