>> Then a complete set of messages:
>>
>>   Copy: 3 files done
>>   Copy: 2 of 3 files skipped
>>   Copy: 2 of 3 files failed
>>   Copy: 2 files in 3 requests failed
>
> What is the difference between the last two?

The latter is used for recursive operations.

> What about the current existing messages when
> there are failures, telling you to use `?' to
> see the details (the `dired-log' output)?

This is now unified as well: