I have managed to free up a little time this morning to put something "rough and ready" together to highlight why I am convinced that your i1 Display Pro is not introducing defective near black readings into your profile/LUTs in the way that you may think that it is.
Let me explain....
The i1 Display Pro, when using it on its own with no other meter to profile against for reference, will typically measure a WOLED panel anywhere from around 6% - 12% brighter than a higher end meter. As an example, here is a screenshot of the Jeti and i1 Display Pro BPD data that was created during a recent probe match I did (when I probe matched the Klein and i1d3 to the Jeti simultaneously).
Jeti data on the left, i1 Display Pro data on the right. As you can see, the i1 Display Pro measures brighter. But this is just with four colours, right? 94% Red, Green, Blue and White...So what about the rest of the millions of combinations? Well, over a 1000 point measurement profile comparing the unmatched i1 Display Pro (Generic CMF) to when Probe Matched has been applied (FCVM) the difference in luminance values is consistent with what you find in the probe match data seen above.
Here is an example of such a comparison showing just the low luminance reads of the 1000 points, and white, with the absolute difference, the percentage difference, and the average over the 1000 points.
I can provide the excel if you wish to look for yourself at the rest of the 1000 points, but I can tell you that it is consistent with what is shown in the image over all colours throughout the luminance range (as expected).
But that means nothing really, because it doesn't prove that the i1 Display Pro isn't introducing defective near black measurements into your profile/LUTs. And you'd be absolutely right to think that...You would have to compare it to another meter that has been proven to handle low light luminance readings to show that.
So here is where the Klein K10-A comes in. As I stated in a previous post, I created a simultaneous probe match with both the Klein and the i1 Display Pro to the Jeti. I then made 1000's of measurements ranging from simple quick profiles, to 1000 point cube sets, and even a full display profile with the patch sequence provided with the LG OLED guides. For simplicity sake, here is a screenshot showing some near black comparison measurements between the probe matched i1 Display Pro and the probe matched Klein K10-A.
I did this in Full Range to provide more steps out of black. It is only for comparison purposes, Full Range should not
be used for LG OLED LUT calibration.
Below 0.02 nits was left out of the sequence as the i1 Display Pro is never going to get that low, but as you can see, from 0.05 nits and above the i1 Display Pro compares favourably to the Klein K10-A, and although there is variation, that variation is well within the NIST tolerance level of 1.5% luminance error.
If you combine this knowledge with the fact that the provided patch sequence for LG OLED calibration has only 3 patches that could potentially measure below 0.05 nits (based on a peak 100 nits, 2.4 gamma), then there is no way that the i1 Display Pro is introducing any defective near black measurements into your display profile/LUTs.
Here is that patch sequence again with the potentially troublesome patches highlighted (again, they are not troublesome at all).
There are only 3 patches in that sequence that could be considered "out-of-reach" to the i1d3, with a further 3 patches "borderline". As I said before, delete them if you are concerned.
Now, considering you are probe matching your i1 Display Pro to an i1 Pro Spectrophotometer, what I would suggest is that you compare the luminance readings of 94% RGBW with your i1 Pro Spectrophotometer to your astronomy camera, because if anything, there it where your luminance differential is coming from. When you have done that, it then becomes a choice as to which meter you decide to trust more when measuring your WOLED. The i1 Pro Spectro, or the astronomy camera?
If it helps in making your decision, when I still had my i1 Pro 2, I compared it to the Jeti and although there was a difference in the xy coordinates (as expected due to 10nm vs 5nm), the luminance was very close in comparison.
Basically, what I am trying to convey here is that your i1 Display Pro is not introducing defective near black readings (not in the way you may think that it is)
provided you use the patch sequence provided, and if anything you should be looking to your i1 Pro or your astronomy camera and deciding which of those to trust. But even with that considered, the fact that above black (17-27, or whatever) looks darker than on an uncalibrated mode does not mean that it is not more accurate to how it should be, and none of this is even taking into account the potential of the near black bug contained within the firmware of 2019 LG OLEDs.
I hope that clarifies as to why I was so adamant in saying what I did before.