Cant remember the exact date, i can have a look through my email folder. But very confident it was some time after the date you bought yours. Have a look under the motor, it is stamped on the ESC circuit board toward one side in white letters. Remove the 4 screws that hold the carbon plate to the plastic arm that the motor is held on to. You can then lift the whole thing up, it is just connected via the 3 standard motor wires, you can then easily see which version of the ESC it is.
It may well be even though it is an earlier one, it is perfectly fine to use, but it is a risk. I think at one point there was a 50/50 on the first batch of S800's as to wether the user would experiance any issues in flight. Most times it was after a fair number of perfect flights. But like i said, after the new ESC's, and with the updated V2 GPS sensor, they are pretty stable nowadays.
It might also be worth updating to the V2 IMU, i think a lot of places are doing good deals as an exchange program (Around £160 when handing the V1 IMU in. A new IMU is about £480). But this is really only needed if you experiance height hold issues, or erratic vertical movements.
