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).
Terrence has been slowly declining from its former popularity. All-time it's been given to 181,160 U.S. babies, the 1,389th most common name by sound today, peaking at 3,511 in 1964, with 263 in 2025.
By sound, Terrence also includes the spellings Terrance, Terence, Terance.