Avengers 83 isn't the first appearance of a character, just the first published depiction of a character's likeness - as portrayed by an impostor. You might as well just go full Ween.
Really now, you haven't even read the issues you're discussing, have you?
In all 3 of the first appearances, the Enchantress is the one to give the Valkyrie's likeness/personality/powers to each character. In Avengers 83 she used the likeness on herself against the Avengers. In Hulk 142, she used the likeness on Samantha Pennington to attack the Hulk. In Defenders #4, she again used it on Barbara Norriss to help her with the Defenders.
What in the world is the difference?
But in Hulk #142 and in Defenders #4 the Valkyrie is effectively taking the place of the two women, while in Avengers #83, if I recall correctly the Enchantress is just appearing as the Valkyrie, but the Valkyrie is not there.
Definitely the Avengers #83 needs re-reading, but anyway they are all important to me. (thumbs u