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).
Sandra was more common in the past and has since settled at a lower, steady level. All-time it's been given to 878,223 U.S. babies, the 1,675th most common name by sound today, peaking at 34,852 in 1947, with 188 in 2025.
Sandra has no common alternate spellings by sound.