could have done一般是指原本有能力可以做某事,结果没做成.往往是现在对过去的懊悔.couldn't have done指不可能做某事,是表示否定的猜测.
should have done 本应该做某事的,现实情况是没有做 shouldn't have done本不应该做的事,现实情况是做了