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).
Joel is now well below its former popularity. All-time it's been given to 282,250 U.S. babies, the 441st most common name by sound today, peaking at 4,661 in 1985, with 1,639 in 2025.
Joel has no common alternate spellings by sound.
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).