Why do you think, that DF-21D is untested?
But has it really been tested? Yes, we know the missile the DF-21 works, that is not in question. However, has it ever once fired and hit a target moving in a random direction that is located and tracked from over the horizon? No, it has not.
In fact, it requires a large chain of things to happen, and all happen precisely. Including things that are just not possible. Such as being able to build an over-the-horizon RADAR system that can locate an object over a thousand kilometers away to within 50 meters of accuracy. And it then must be able to constantly update the course of the missile, which is traveling at MACH 8+. And be able to adjust it's course to an accuracy of 50 meters.
Oh, and do this against a target that is constantly moving and changing course, at 30+ knots. ANd still get through all of the defenses (both physical and ECM) to actually hit the target.
This thing has as of yet only been used against stationary targets on land. They have it a "carrier sized" target in the Gobi desert with it, but once again that is not a surprise because it is possible even with the original DF-21 missile. The target was not moving, and in their own missile range.
And yes, I know about that NOTAM. Once again, so what? It shows they did a missile test, that is all. Most speculation is that they fired it at one of the small islands that are scattered in that area, what does that prove? Once again, that they could hit a static target inside of an area that has tons of conventional RADAR coverage.
Not a moving target, not a target over the horizon.
This is why it has not been "tested". This is a "weapon system", and until the entire system is tested it is "untested". The DF-21 series of missiles is over 35 years old, nobody questions that the missile itself actually works. The big doubt is that the system itself will never work.
And until they can prove they can locate, target, then hit a moving target from over the horizon it will remain nothing more than a magic trick.
Not to mention the even bigger problem with this system. In flight, this is no different than the DF-21A/C missile. And those are armed with 500kt nuclear warheads. A great many believe that this weapon may not even exist at all, and simply be a cover to slow the reaction of the US for when it may decide to launch a nuke at one of our fleets. And even worse, if a group has already been given freedom to use it's own nukes they might respond with a nuke, no matter which variant of DF-21 has been launched at them.
But why you are taking a simple NOTAM and trying to scream it proves the weapon system works I have no idea.