As you suggested, I will consider your question in the context of a past event.
1) I don't understand how you could have missed that.
Here, you are talking about a specific event and what happened that resulted in me missing something during that event.
A possible expansion and rephrasing of the sentence could be:
I understand how you might have missed that in other circumstances, but how did you miss it in those circumstances?
2) I don't understand how you could miss that.
This construction has several differences from the first.
Not only are you talking about an idea in general, rather than a specific event, but you are also not necessarily talking about me and could be using you in a generic sense.
In other words, it could be rephrased as:
I don't understand how you or anyone could ever miss that in any circumstance.
The same analysis could also be applied, respectively, to your could have gotten and could get example sentences.