Let's play the devil's advocate . . .
A "cameo" cannot be a 1st appearance, as the character must have already appeared and be known to the viewing public to appear in a cameo appearance.
The first time a character appears within a story, and is identified by name, constitutes the first appearance of that character (regardless of scope or breadth of appearance.)
Any brief appearance of a character thereafter in a story (not on the cover) is a "cameo."
Any 1st appearance of a character on the cover is a 1st Cover Appearance, and ultimately, is the appearance of the character that SHOULD have the most value, by ANY metric.