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).
Gail was a common American name in the 1950s but is rarely given today. It's been given to 309,349 U.S. babies all time and once ranked 284th by sound, peaking at 14,138 in 1951 (down to 25 in 2025).
By sound, Gail also includes the spellings Gayle, Gale.
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).