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).
Joy was more common in the past and has since settled at a lower, steady level. All-time it's been given to 156,110 U.S. babies, the 753rd most common name by sound today, peaking at 3,095 in 1957, with 889 in 2025.
By sound, Joy also includes the spellings Joi, Joye, Joie.