The Modal Auxiliary + Have + Past Participle type construction (Modal Auxiliary + Perfect) allows us to speak retrospectively about a completed action in the past:
Example :
1. It must have been hot last summer. I imagine that it was probably hot last summer.
2. They may have crossed the border by now. They might have already crossed the border by now.
3. You might have missed a very good opportunity. It's possible that you have missed a very good opportunity.