Thanks for your responses, I will investigate. I am surprised that my x-rite ColorMunki Photo and now Calibrite software does not have some basic verification step to measure the "offsets", and maybe compare with the previous "offsets". From what I know human vision is pretty good for relative before-after or side-by-side measures but not absolute measurement. Thanks again.
The verifications are usually just feel good approaches and not useful (I'd put the BabelColor as exception).
TThe validation is, by and large, only useful to determine when the process doesn't work correctly, and you want dE numbers to back it up. It isn't useful in gauging overall accuracy for a number of reasons. First and foremost is the issue is that you're using the same software and, more importantly, the same measuring instrument for both the calibration and validation, not a higher-grade reference device, to gauge accuracy.
As an analogy, suppose I measure my foot with a $2 wooden ruler from a hardware store and find it's 10.7 inches. Clearly, my foot isn't an accurate measuring device compared to that 1-foot wooden ruler. But how accurate is that $2 ruler? It, too, should be of sufficient accuracy for the task. There are devices like a 50-cent wooden ruler that may be accurate to +/- 1/10 of an inch. For measuring a 100-foot fence, that may be all that's needed in terms of measurement accuracy. For measuring a component that will be used on a spaceship headed to Mars, 1/10000 of an inch may just be adequate enough for the specifications of the job. But my 10.7-inch foot clearly isn't accurate. So when we talk about accuracy, we need to take into account the instrument used and the method of measuring the accuracy. And how accurate we need the results of the measurement to the reference. With dE, 1 or less is invisible. And the formula used, which differs, is also important. We are using the same instrument to evaluate the display accuracy, and that's not worthless but not ideal either.
Then we measure one area in the center of the display. What about each corner? Again, the dE reports provided by the software are probably useful when you see a really large dE (well over, say dE6). That could indicate something went wrong when you were calibrating/profiling. The screen saver came on, the software had an issue, the instrument fell off the screen, or some large amount of ambient light was measured. If the dE report is that high, you'd probably notice it anyway. So take the report with a grain of salt.
The other issue with some products providing such a report is they don't use too many color patches; they pick patches that are easy to produce and avoid those that could produce a lesser "ideal" report. Think dark saturated colors. And they often don't measure enough color patches to provide an average deltaE report for some.
Now what IS useful is known as colorimetric trending! That's where the same product reports the results over the course of time (say once a month over the course of a year). It tells you how often the display has changed if you calibrate every month and by how much in deltaE. It could be useful in deciding that instead of having to recalibrate every month, you can get by once a twice a month, or maybe you need to do this every few days. The inaccuracy of the device compared to a reference isn't a factor as long as the consistency in its measurements is good. And it should be, although not all available instruments are sadly.