How to apply a unique listing no to entries..

How to have the post_id appear in the Listing manager edit mode..

I am trying to use the post_id number that is generated with each listing to appear on the listing printout named as Listing ID:
I managed to get it to work.. But it appears that while all the listings as they appear in the Listing Manager has that identifier ID.. when you look through the listing in edit mode it is not there as a field.
It used to be on some of the earlier listings and I can add it as a custom field and then it shows in in the edit mode and it will appear on my printout..

But how come that post_id field does not show by default in the edit mode.. as does for instance ‘visitorcounter’ which is not a field that the user adds..

I am confused .. hope someone can set me straight on this.. and the same seems to be the case for both ID and post_id.. both of which incidentally show up on the exported csv files.. one at each end of the record..