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).
Marcelo has been climbing in recent years. All-time it's been given to 13,231 U.S. babies, the 895th most common name by sound today, peaking at 798 in 2025, with 798 in 2025.
Marcelo has no common alternate spellings by sound. Spellings sometimes heard the same way: Marcello.
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).