If the bottle has never been opened there is no need to do anything like mixing it with a new bottle. The enemy of glow fuel is moisture. If the bottle is never opened it has no chance to accumulate any moisture. As Gray Beard stated above, even opened bottles will last for a long time if the bottles are kept tightly sealed and only opened to pour out fuel. I've had a bottle of fuel on the shelf for over 5 years and when opened and put in a plane it ran like a brand new bottle of fuel. As stated many times, the key is keeping sealed.

Ken