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).
Thea
Thea has stayed fairly steady in American naming for generations. All-time it's been given to 20,118 U.S. babies, the 699th most common name by sound today, peaking at 1,209 in 2018, with 867 in 2025.
Thea has no common alternate spellings by sound.
Rising