I came across a situation where user is trying to search documents selecting the option "search in same site" instead of "all sites" from search box and getting no result where as can find documents from other library with in same site.
Why such happens ?
The first point comes to mind for search error is content not crawled, indexing not done for this situation.
Yes , its true but we need to think why ?
As per my investigation I found the setting of the library as below
By default SharePoint only crawls major versions of files and draft items are only viewable by their creators. SharePoint is behaving as expected out of box.Draft items are not crawled in SharePoint
This behavior can be altered in Document Library Settings -> Versioning Settings -> Draft Item Security
Select the option "Any user who can read items".
This will allow all users to see draft items including the crawling account.
* Else you need to select "Create major versions" option or can publish the documents as major versions if want to get those documents in search result as per client wish.