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).
Joe was more common in the past and has since settled at a lower, steady level. All-time it's been given to 645,485 U.S. babies, the 1,454th most common name by sound today, peaking at 14,885 in 1947, with 274 in 2025.
By sound, Joe also includes the spellings Jo.