This case is not handled by default deploy plugin, as it does not support "local staging". This is about ["two shots"](https://docs.sonatype.com/display/Nexus/Staging+V2+Testing#StagingV2Testing-%22Twoshots%221stpass%28deferringuploadintoanother%22pass%22%29) invocation, something like this:

```
$ mvn clean deploy -DskipRemoteStaging=true
...
BUILD SUCCESS
=============

$ mvn nexus:deploy-staged
...
```

Now, the "index file" is needed to re-construct all the Artifact and Metadata instances created (and locally staged) in first shot, where the build actually happened.

We could do something similar as vanilla install and deploy Maven plugins got implemented recently (basically "deferred deploy" mode of this plugin):
http://jira.codehaus.org/browse/MINSTALL-93
http://jira.codehaus.org/browse/MDEPLOY-157

But it works only in "one shot" mode, when build and remote deploy happens in same maven invocation...