Uses of should have been

Question

Context is, invalid proof approved instead of rejection. Then what would be the interpretation of below sentence.

"Proof should have been rejected"

Interpretations

1. Proof should have been rejected , and it is rejected.

2. Proof should have been rejected , not sure about the result.

Answer 1

"Proof should have been rejected" is simply an opinion about whether or not Proof was good enough to be approved.

While not explicit, it is often used to imply that Proof was approved, and that [speaker] disagrees with the outcome.

That said, saying "Proof should have been rejected" even though Proof was rejected CAN be valid. It could be used as an emphatic agreement with the outcome of Proof having been rejected.

So, it does not explicitly mean that Proof was rejected on its own. More context is needed.