Good question! I think that in your example, the enemy will see only the armored car. But I wait for a veteran answer too...

They will be invisible until close combat.

they will only see the armored car , till they start fighting or till an enemy unit with a higher exploration or same level as your commands appear

I can confirm that, stealth units will remain invisible until close combat.
This can be absolutely devastating.
Nothing worse than attacking a single unit, with the numbers and terrain in your favor...
... and then getting punched in the mouth by a stack of high-level AT guns or militia.
It can really mess up your war plans

your entire border and all your units in enemy territory should be within AC, INT range. This is part of the air game also to prevent being patrolled by "hidden" enemy airplanes.

You can see "invisible" slow units sometimes by the speed of the stack/unit, if the player is not able to play it well enough.

Actually Stealth units such as Commandos and Paras can in a way be detected in a stack without any Scout units observing them. Here is how, if you stack a unit of Commandos with a group of Infantry and then attack and take an empty city or province the newspaper report will identify it as 20th Commando Division captured London. The report will not tell you if there is 1 or 9 Commandos in the stack but you will know that there are Commandos in that stack. This should be fixed so that Newspaper reports are either ALL generic in what unit type captures a target OR the Newspaper report say the 20th Infantry Division captures London.

The newspaper is very useful in determining what type of units some nation is using that you're not really in contact with (yet), exactly by the names of the units capturing cities. There's a huge difference if it keeps talking about the "9th heavy tank division" captruing locations in several reports (this is a slow player who doesn't really use a front screen of light armor) or if it says the 4th, 13th, and 17th armored car brigades each took a province (a potentially very dangerous opponent, who knows how to veil the moves of his "real" units). I wouldn't really support using some generic naming thing ("Cairo was captured by the 3rd unit").

Here's what I do: the Anglerfish Defence.
In 1.5 at least, stealth units even when stacked with non-stealth are invisible until engaged or scouted.
As such, a fairly good defence can be made, which not only is effective but breaks down enemy morale and induces paranoia:
1. Take 1 non-stealth unit (e.g., an obsolete lvl.1 light tank). This is your lamp; nice juicy bait for enemy heavy armour.
2. Stack it with 4 anti-tank guns. These are your jaws.
3. Place it at a choke point to hold him up for a while. If enough guns, can hold him for hours.
4. Lure him into the trap.
He'll think twice next time.

Absolutely! Works best with cheap defensive units researched to a high level. Level 4-5 militia and AT guns. Bait with an obsolete plane, or LT, but be careful you don't invite air attack. A smart enemy will not waste time researching level 4-5 AC's or Mot Inf just for scouting, he will use level 4-5 fighters and the jig is up

Why would you bait with a plane?

The point is to bait with something weak and useless.
An outdated, damaged plane will do just as well as an LT.

But how? You can't stack it with anything.

You can just put it on an air strip together with the ambush units...?

Sorry for a tangent here, but on the subject of Stealth Units....

If a stealth unit is undetected at a province dot, and that dot is brought under ranged fire (any of plane, ship, artillery, rocket, bomb), will the unit be damaged?

How about "splash" damage (I think nukes have an AoE effect but I may be mistaken).

It does when there are other non-stealth units in the stack (the damage gets distributed and it takes its share of the damage). When the enemy doesn't "see" a stack, no.

I thought the idea was to stack them. But if it works it works.

@K.Rokossovski if so that would be really illogical. When I let a artillary division fire into an area I would suspect at least minor losses at enemy forces.

Yes and no. On a small scale, if artillery fire into a small town in the center of a province or at the airport where suspected defenders are hiding, there should be some casualties just like there is collateral damage to buildings.

But that's not how CoW works. Map tiles represent large areas tens to hundreds of kilometers across. Even if you know there are rebels somewhere in greater Los Angeles, do you really expect an artillery or air bombardment to hit them randomly? Not really, the area is too big. Once your forward observers spot the likely location of the enemy, then you have more of a shot at hitting some of them.

If anything, indirect fire is OP in the game. Artillery barrages and tactical bombers runs work against massed enemy formations. A few remnants of an infantry regiment hiding in the forest after being beaten and chased out of a city are not going to suffer much, because they are already dispersed and not putting up much resistance.

Some function taking enemy HP and fighting strength into account is needed to approximate this effect of artillery working to disrupt massed enemy formations most vulnerable to indirect fire. Indirect fire should work best when concentrations are highest, and direct attack should work best when the enemy is scattered and weak. This would be more realistic and it would promote more coordinated, combined arms attacks.

In fact there were war games in the past that used artillery and air as modifiers, helping the main land-based attack. These modifiers represent a combination of with spotting, cover fire, smoke, disruption of movement, disruption of supply, etc. This made air and artillery very interesting to use, because it greatly increased the odds of success without turning into an OP standalone method of destroying entire armies.