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).
Nikolai
Nikolai climbed for decades and has been a steadily popular name ever since. All-time it's been given to 11,027 U.S. babies, the 1,081st most common name by sound today, peaking at 639 in 2016, with 469 in 2025.
Nikolai has no common alternate spellings by sound.
Rising
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).