@delaro plenty of mining cards won't have been BIOS modded. In general, I don't think BIOS modding is a thing for Nvidia cards the way it is for AMD. For Nvidia, you would just adjust clocks/voltage with a software OC tool.
Other than BIOS modding, I don't think any of the other things you listed could prove the cards were mining. They could maybe prove the card was frequently under heavy use, but I don't see how they could determine what sort of use that was. Maybe the user spends a lot of time gaming, maybe they use the card for rendering for extended periods of time, or runs folding@home whenever the PC isn't in use.
Also depending on what you're mining ( especially eth), the cards may be underclocked and/or undervolted. So it's not as easy as just looking for cards that have been heavily overclocked and/or run at their limits.
I don't understand what you're saying with the "time on a different status" bit.