The first sentence is stating a fact.I'd like to know the differences between the below sentences
Sarah couldn't have got my message.
Sarah mightn't have got my message.
Hello. I would like to first say that it should be "gotten" instead of "got"
Sarah couldn't have gotten my message= There is no possible way that she has received the message
Sarah might not have gotten my message= You're not really sure if she got the message or not.