Understanding “Couldn't have got”

Question

Here are two sentences:

Sarah hasn't contacted me. She couldn't have got my message.

What is the correct meaning of the above?

1. Since Sarah hasn't contacted me, there's a possibility she missed my message
   (the same meaning as “She must have missed my message.”)
   OR
2. Sarah hasn't contacted me BECAUSE she couldn't have got my message for some reason

Answer 1

Sarah hasn't contacted me. She couldn't have got my message.

Suggests that the speaker believes or assumes that Sarah didn't receive the message, because if Sarah had received that message, she would have replied to the speaker.

The speaker is speculating as to why Sarah didn't reply. If the speaker wanted to express uncertainty then she/he would say:

1. She might not have got my message.
2. She may not have got my message.
3. Perhaps/maybe she didn't get my message.

The modal verb could in its positive form expresses uncertainty

4. She could have got my message
   (there's a possibility Sarah received the message, the degree of uncertainty can be inferred by the speaker's intonation)

When could is used in its negative form it expresses a negative deduction or something that didn't happen in the past (couldn't + the perfect infinitive).

5. She couldn't have got my message.

Here the speaker expresses the conviction that Sarah did not receive the message. The same meaning is conveyed with can't have + past participle as in

“she can't have got …”; “she can't have seen …”; “she can't have read …” etc.

Answer 2

The previous answer seems far sufficient for this question. I just would like to note that I believe it should read "couldn't have gotten" as the past participle of get is gotten. This is especially indicated by the fact the statement implies a perfective acquisition rather than present possession(in which it would be correct to say "I got" meaning I have in my ownership).

(The Cambridge Encyclopedia of the English Language)