Finding a design that overclocked an ADC by 2.5X is just bad design practice for any product that sold to the public, unless there was some "special" feature of this ADC that nobody knew about that allowed this overclocking without disastrous results, why I asked what ADC this was!
This ADC, widely used by many cheap scope manufacturers, is AD9288.
It is designed for 100MHz clock. All these versions, 40, 80 and 100MHz are same design, same silicon, same product. There is ONLY one original AD9288 designed chip.
So, What are these 40MHz (80 and) and 100MHz ADC's.
Analog Devices have designed and manufactured ADC, product AD9288 what is designed for 100Msa/s.
But, manufacturing process output is some amount of 9288 chips. Still all these are same chips.
But all chips do not meet every single specifications what are set for 100MSa/s desing.
After they are made they need test. Some chips meet these specs and some not.
Do they throw away these what do not meet specs. No, they sell these.
So there is other specs, for 80Msa/s and for 40MSa/s
Chips what do not meed 100M specs may meet these others specs... after then most of manufacture process output can sell.
They get -100, -80 and -40 marking.
Most of chips what have -40 mark works normally in digital side just with 100M clock, even more. But they do not meet AnalogDevices specs for AD9288 -100. They work but not meet specs.
If now someone set different specs what is enough for his own purposes he can of course use -40 classified chips with higher freq if they meet his own needs.
When Rigol or who ever use these they did not sell AD9288-100 chips with 9288-100 specs. What they sell was and is oscilloscope with they own oscilloscope specs and what is inside oscilloscope is as it is... they sell whole oscilloscope with this oscilloscope model description and specs independent of what is inside it. They do not sell capacitors or named AD chips.
They can fill whole internal even with black epoxy. They sell oscilloscope with its specs and promise it meet given specs. This is what buyer buy and nothing else. It can include what ever except illegal forbidden things.
Not so seriously but...
I do not even know if it is soon more wise to make oscilloscope what is just permanently enclosed so that it can not even repair or open. Just if failure inside warranty time then just give new one and destroy failed. This can divide two or three parts, "black box" scope main unit and "black box" control panel and "black box" display unit. Three black boxes connected mechanically together and data bus between them. So no matter how it is done or what components they have used inside, under clocked or over clocked.