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).
Joyce was more common in the past and has since settled at a lower, steady level. All-time it's been given to 512,232 U.S. babies, the 1,586th most common name by sound today, peaking at 16,807 in 1942, with 233 in 2025.
Joyce has no common alternate spellings by sound.