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).
Thomas was more common in the past and has since settled at a lower, steady level. All-time it's been given to 2,367,087 U.S. babies, the 84th most common name by sound today, peaking at 48,725 in 1952, with 6,924 in 2025.
Thomas has no common alternate spellings by sound.