Well, except for those of us who think it should be...
Marvel Preview 7 - 'First Appearance of Rocket Raccoon' Summer 1976
IH 271 - 'Second Appearance of Rocket Raccoon' May 1982
My point is Marvel Preview #7 is the first appearance, although a magazine. Some people pimp IH #271 as the first comic book appearance of Rocket Raccoon (with a cover appearance). However, MP #7 is more valuable. Yet Marvel Super Special #16 (magazine) is the first appearance of Boba Fett, but Star wars #42 is more valuable. The same logic does not apply. Yes, the market will decide, but sometimes the "rules" are as clear cut as you think.