Aggregate tag lists for completion in orgmode

I would like that the tag completion mini-window aggregates :

• buffer tags defined in #+TAGS header (LOCAL_TAG_1, LOCAL_TAG_2)
• tags set in the previous headings (ANOTHER_NEW_TAG)
• tags coming from the variable org-tag-alist

In this simple example :

#+TAGS: LOCAL_TAG1 LOCAL_TAG2

* Heading 1 :ANOTHER_NEW_TAG:
* Heading 2 

The completion window is actually showing only :