Yes, but these ADC cores are designed to meet the specifications of the end goal which is to have and ADC with X bits and not X+'magic number' bits.
Anything beyond is just luck. If you buy a whole bunch of 3.5 digit DMMs and stick 3 extra digits to them, a few may seem to be accurate beyond 3.5 digits but that is more due to luck and cirumstances (right temperature for example) rather than solid engineering. In the end measuring is about having a certain confidence level in what is being shown on screen.
The same goes for measuring signal levels using an oscilloscope. The numbers Performa is listing in a posting above, have a 0.5dB error margin. IOW: a different unit may show different results within the specified error margin.
This
IS the way things work, whether you want to believe it's due to "magic" or "luck" is of course your prerogative.
The mentioned 24 bit DS ADC just uses a 1 bit comparator (ADC if you will), yet achieves better than 20 Effective Bits (ENOB). This is achieved, even specified in the data sheets, using Oversampling and Decimation, basic Signal Processing 101 methods.
The idea of "dithering" to achieve higher resolution and improve linearity is not new, this was utilized in the early 70s in the Ring Laser Gyro (RLG) to "unlock" the counter rotating photon (laser) beams at low rotation rates (dead zone), and likely utilized well before this time. Don't think folks back then would rely on "luck" or "magic" to guide/navigate an airplane, ship, submarine, satellite, rocket or missile.
So the techniques being discussed are real and repeatable, not conjured up non-sense as we often see. As much as many like the Siglent DSOs (we have a couple), the results shown are not unique to these instruments, but achievable and repeatable by any quality DSO with the necessary features to achieve such, and would expect the Rigol, GW, Keysight, LeCroy, Tek and so on, would respond similarly to these techniques.
Anyway, hope you'll realize this isn't "magic" nor "luck", just good old Engineering/Science Signal Processing being put to use for our (and others) benefits.
Best,