How to read the band →
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).
Joan
Joan is now well below its former popularity. All-time it's been given to 488,939 U.S. babies, the 1,212th most common name by sound today, peaking at 21,132 in 1932, with 454 in 2025.
Joan has no common alternate spellings by sound.
Rising
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).