Alright, sorry... I didnt want to have to do this. But the Sherlock Holmes in me couldnt resist.
I pulled up some pics of my oem s13 silvia fenders as well as non oem (overfenders/vented). Both oem and aftermarket silvia fenders have a factory body line that runs along the "entire" fender. Matching the factory line that runs through the doors as well as the the rear fender.
(Here is a picture of my oem silvia fender) Notice the body line i speak of.
Now the difference on the oem/aftermarket 240sx (usdm s13), the body line stops before the front wheel. Notice below.

Aftermarket overfenders 240sx (usdm s13)
Now, the method to my madness. With closer observation of KingDutka's s13, the fender in the picture possesses that factory body line. Refer below.
In conclusion... those fenders, or at least the one shown is an aftermarket fender for an S13 Silvia. I rest my case.