I missed this post earlier, sorry.
Wake-up probably does break down over time, depending on the sunlight and temperature where it is stored. It also contains some alcohol that prevents biological growth in the bottle, such as algae or bacteria. I'm guessing yours has been stored inside and may not have been exposed to the conditions that contribute to its breaking down. Since it seems to be working, it probably is! I will see if I can find out more from the manufacturer and let you know what they say.
Charlie
O Ok cool , its been stored under my sink the whole time, It does seem to be working so its probably still good. I bought some more just in case.