ECU with Performance Upgrade Flash?

[MB-Dude]

When I purchased my '96 SL600 from a third party about 4 years ago, the car ran great. What surprised me was how responsive the throttle was - touch the accelerator pedal at virtually any speed and the car seemed like it would 'leap' forward. (This is a good thing!) But... the car failed a California smog inspection with a number of 'Not Ready' registers in the ECU. No Check Engine Light, however.

After months and $$$ of fruitless troubleshooting by an MB Dealership and myself, what seemed to solve the ECU Register 'Not Ready' issue was 93 octane fuel. I had been running exclusively 91 octane fuel (best premium available in CA.) Only the fuel change made the difference and that was about 18 months ago. Car continues to run awesome. (I posted details of this problem in other threads.)

As I was reading various topics the other day, it occurred to me that maybe my ECU's (my V12 has a pair of them; one for each bank) had been performance-enhanced through ECU reflashing by a previous owner. My thinking was that maybe because the ECU’s were optimized for a higher octane fuel, that that was the reason for registers ‘Not Ready’.

Question - Is there any way to tell, electronically, if ECU's have been flashed for performance by 3rd parties?

I had occasion to physically open each ECU during the above mentioned troubleshooting and there were no obvious indications of non-MB work. Although at the time I was not specifically looking for that. Since the car is currently running very well, this is more of a curiosity question.