There really isn't a way to tell. You can try contacting Eleaf with the numbers on the box and they may be able to help you(fat chance of them actually helping), or you can just use it. I got mine back in march and it has been flawless. Several people have had the same experience. At the same time, several people have had serious issues with theirs. Even though I never had any issues with mine, I recently bought a Sigelei 150w to take over as my main device. I really just wanted something with more power available so I could go with bigger builds. I still use the istick pretty much any time i go fishing, though. I only charge it in a 50 cal ammo can with the lid just lowered down(not latched closed) on a concrete floor just in case it would vent. I wouldn't recommend charging it overnight. Also, when you are done with it, take the atomizer off it just in case it decides to start auto firing.
As for the resistance, the coil could just be reading a bit high. It isn't uncommon for coils to be a bit over what they state. Out of all the coils I have tried for my subtank mini(I only use the 0.5 ohm OCCs), they have all been 0.6 with the occasional 0.7. When the wire heats up, the resistance can fluctuate a tiny bit. As long as it isn't bouncing around more than 0.1 ohm, I wouldn't really worry too much about it. There really isnt a way to fix it. Your device could just be reading a little high, or the coils could just be a little high, or a mix of the two.