The internal IF AGC of the ADC will not allow any digital saturation to happen. It will silently adjust the level at the input of the ADC and keep the signals below 0 dBFS. The same applies to the RF AGC chain plus or minus the threshold level. This excludes many of the assumptions stated in the previous emails.
What could happen, however, is all these non-linearity problems that could be introduced by bad contacts (mostly in connectors), bad cables, and even rusty metallic structures surrounding the antenna that could mix signals and translate them into unexpected frequencies. Here's an example from the recent memory: https://www.pressreader.com/canada/windsor-star/20191009/281517932872802
I have seen this happen too many times to ignore it. Many experienced ops overlook these details. Even Leif found some noise humps (similar to those we see in these screenshots which are unaffected by the attenuation level) when testing the original HF+ and he traced them back to a faulty (leaky) attenuator. Once he replaced the attenuator, things went back to normal. At the same time, I am being realistic by not expecting everyone to have Leif's experience. Someone else would have just trusted his apparatus and produced a bogus appreciation.
This is the main reason I do not take anyone's tests on their face value. Understanding the phenomenons involved in the "bad" results and being able to reproduce them is proper engineering. The rest is, well... just noise.