Oils viscosity is tested at 100*C, AKA operating temp. Oil tests do not normally test the cold viscosity wich is represented by the lower number, but my guess is no. When people speak of oil thickening with age they are talking about the high number which represents the oil's viscosity at operating temp.
On lesser oils, the base stock is not as pure as AMSOIL and it has molicules of different sizes. As the oil is used some of the base stock is cooked off or evaporates as fumes and vapor. Since the smaller molicules are lighter they are the first to get boiled off leaving the larger thicker ones and that is what causes lesser oils to thicken with age. AMSOIL's is all the same size so as it is boiled or cooked off, it leaves behind molicules of the same size so there is no viscosity change.
I have run AMSOIL Series 2000 0w30 for as long as 18,000 miles in my supercharged 4Runner and I had the oil tested. It reported that it was still good for continued use and it was still a 30w oil, no thickening at all.
You can go to my website and download The Motor Oil Bible and read it. Once you do you will know more about motor oil the 99.9% of the professional mechanics out there. You will also understand how AMSOIL can be safely used for longer periods then the "other stuff" out there.
Gadget