I think you're splitting hairs. Any motor oil, conventional or synthetic, straight weight or multi-weight, will increase in viscosity when progressively cooled. Someone would have to show or direct me to research findings that conclude storing virgin, sealed motor oil at sub-freezing tempratures permanently affects its flow characteristics when warmed back above freezing temperatures. As for used motor oil, all bets are off. As oxidation products form, and the lighter components evaporate off in use, motor oil will demonstrably thicken in viscosity over enough time - dino sooner than synthetic, but it WILL happen, regardless, subsequent to the shearing that results in temporary decreased viscosity.
I dont think you have anything to worry about....
Its just like the oil that has been sitting in the pan overnight at -25*C (it gets that cold here...)and most locals just start the car and drive off in the morning..
If you are talking just about oil -storage-.. it wont make a bit of difference, unless you plan to do an oil change at -25... Brrrrrrr... did it once... never again..
I seem to remember reading here at BITOG that the cold flow properties of multiweight motor oil deplete whenever it gets "cold enough", whether the oil's in the crankcase or sealed in the bottle/jug. If I have this wrong, someone please set me straight.
Assuming this is true, would it be better to store oil inside the house, where we'll assume the temp remains well above freezing? Or am I splitting hairs here? Some of this oil is already a couple/few years old(Lubro Moly 0w40 SJ synthetic), it'll probably be 2 yrs or more until I use it all up, & I have no idea how it was stored before I bought it. The jugs were pretty dusty, though. I should also add, our winters here are usually mild. Most years, the lowest temps we see are ~20 deg. F(~-7 deg. C) or a bit under. So, should I bring it in the house, or leave it in the unheated carport closet?