Those holes are not in the case. Those holes are in the Corsair SFX to ATX adapter which has to be purchased separately. I would be purchasing it though, as it is much nicer than the adapter that comes with the Silverstone SX500-LG I would be buying. I actually used this very PSU in my previous build that I sold. The ATX adapter that comes with the Silverstone SFX-L PSU does not have the extra venting holes like on the Corsair. It also centers the SFX-L PSU into the ATX opening. This would be counterproductive in my situation. The Corsair adapter doesn't center the SFX PSU into an ATX opening, it actually has it so the bottom of the SFX PSU will sit where the ATX would and then adds the venting where the extra height of an actual ATX would be.
The Silverstone SX500-LG SFX-L PSU is actually a pretty nice PSU in my opinion. I never had a single issue with it. The 120mm fan is dead quiet when it is actually spinning, which isn't all of the time because it operates semi-fanless. I experienced zero coil whine / electric noise as well. Johnny Guru gave it a 9/10 and stated that it came out of the "Sirfa" factory. Not sure what that means. It is not the 10/10 that they gave my current PSU, but obviously I am not basing my PSU purchases solely on Johnny Guru.
Included SFX to ATX Adapter
Corsair SFX to ATX Adapter
* For those that do not know, SFX and SFX-L are identical in width, height, and mounting hole pattern. The only difference is SFX-L having added length, just like the name implies.