To be fair, it appears as though the overclocking of the ADC was a deliberate strategy that pays dividends big time for them. Remember, Rigol were the first new company to come along and give affordable 1GS/s ADC sampling in a scope, and this is how they did it. There probably was no other easy way at the time?
Only reason for use 40MSPS classified Analog Devices AD9288 chips was reduce manufacture cost for earn more.
It is exactly same AD9288 what can buy 40, 80 and 100 MSPS. These chips are designed and manufactured for 100MSPS.
Then there is set of limits. From process they get different quality of chips. There is nothing wrong to run 40MSPS classified chips for 100MSPS. But who do this he must understand that datasheet specifications are not anymore valid. If this is not problem then go on.
In time when Rigol start this model they can buy 100, 80 or 40MSPS. But price is different.
If Rigol look that 40MSPS classified AD9288 meet Rigol needs (reduced specs) then there is not any kind of problem. They work as Rigol specs for Rigol customers. What is overclocking or "overclocking" in this case - this discuss I do not want start anymore agen.
Only reason for 40MSPS chips was price! Same AD9288 quaranteed meet 100MSPS specs limits was also available fom AD.
-40 chips price is 1/3 what is -100 chips. 15$ only for ADC chi.ps is better than 50$ when whole scope manufacturing costs need keep well under 200$ and there really is also other costs than just ADC chips.. Using these 40MSPS selected chips for 100MSPS meets Rigol own specified needs so theere is not any kind of problem use these. (of course in this case AD datasheet some specs are not valid - mainly perhaps in ADC input T/H circuit. leading poor SNR, SINAD, ENOB. If they meet still Rigol needs it is all what neeed)
About grinding chip label... what is problen there. Nothing. Design belongs to designer and he can hide everything he want. Many big brands haave done this as far as I remember. Not just grinding labels, also using wrong labels, also using more or less secret and later leaked manufacturer own classified codes lists for internal use. Result with consumer eyes is same...
If I buy chips from manufacturer and I want they print my own part number there, I pay and they do. Say example I use AD9288. I grind all label off or other case I have there my own label: JvwLMmwPbCR57Qx3. What is difference?
Other question is what they think they win with grinding or false marking any this kind of component. Who really want and need know, he know. It did not hide anything important example from manufacturers in china who are competitors. Who really think that time when DS1052E was launched manufacturer engineers in China did not know how to do this kind of interleaved ADC for cheap oscilloscope. Really there was not any secret innovations. This was circulating even in school boys exercises. (only what they perhaps try hide they was selected this lowest grade 9288).