You can just say the dates for which you traded different ea's, but to prove an ea's profitability, I guess you would need to open a separate account for that ea.
Yes you could open a new account once you get bad results, but that would be suspicious as it will be visible when did you start trading on the new account.
let's say you're talking to a potential client - he would most likely ask you to see the account traded for real (either with investor password for mt4 or some other way), so why would you want to hide that in the first place?
It's understandable you want to show only the relevant period for your latest ea, but if you could select a custom period to show performance, what stops other from misusing this?
Think about it. I'm sure you'll get my point <img src='