I remember though combat group is consist of only hidden deployment or combat jump(it means, only private information troopers), exist of combat group is open information at N3 rules. But there is no such thing at N4 rulebook and FAQ. So 'Private Combat Group' is exist at N4? Or is there something I missed?
It was definitely open information in N3. I can't remember what the rules wording was. I don't see it explicitly in the N4 rules, but "any piece of information on a player's Army List that is not explicitly Private" is open information. I would say that the existence of a combat group is a "piece of information on a player's Army List," so it would be open information, even if the combat group appears to the opponent be empty. Which raises the question: can you create an actually empty combat group to fake the existence of a hidden trooper? I would say no, because "A Combat Group is a closed group of Troopers," so a group with no Troopers in it wouldn't meet the definition of a "Combat Group."
Looking at it that way.... Taking the last trooper out of a combat group destroys that combat group, rather than leaving it empty. And a new combat group is as easy to create as “I spend a command token to move this trooper (and its peripherals) to a new combat group.”
When I asked this in N3 it was ruled No, and none of the reasons why that would be so save have changed, so concur with your take here.
