typically, I generate the NATdoc for everything in one or more libraries and post it to my shared area with a title and overview. If I then update a few modules' NATdoc and generate those selected items, the title, overview and entries are not there and the resulting view of the NATDoc only includes the latest items generated, even if the check box to "Generate index" is cleared.
With a lot of objects, regenerating the NATdoc takes some time. Being able to selectively update the NATdoc without wiping out what was done before would be helpful.