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).
Declan
Declan climbed for decades and has been a steadily popular name ever since. All-time it's been given to 58,950 U.S. babies, the 257th most common name by sound today, peaking at 4,007 in 2019, with 2,587 in 2025.
Declan has no common alternate spellings by sound.
Rising
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).