Incremental content updates

When we attempt an OS incremental update, it seems to overwrite our existing content rather than adding to it?

What is the correct approach for this?

We started with a full exported content which had over 6000 packages and then the incremental had 13, then our redhat repos were showing 0 where no new packages were found and then just 13 were available when we had re-published a corresponding content view.

Any help would be much appreciated...