There are two reasons why mother's maiden name is not displayed - in some older records the name has not yet been indexed; in more recent records it does not appear for reasons of security. If you look on the Scotland's People website at the search page for deaths you'll find a link to "important information regarding mother's surname".
The "other surnames" would show up if someone had been married more than once. In Scotland, the maiden name would always appear in the index too (as long as it was known).
Lizci