Imagine taking 85ml of castrol gtx and adding 15ml of cooking oil.
Then try mixing it up till you know its gone from 85ml & 15ml seperate liquids to 100ml of a completely blended substance.
You'll find it's really difficult to mix it completely in one go and may take a few days of shaking up every now and again.
Then think about making an aromatic curry from scratch withe several different herbs and spices and notice the difference between eating it fresh and then eating it the next day once all of the flavours have had enough time to completely infuse together.
Mixings no different really in principle with the extra complication of how some flavourings will also change slightly over time.
As long as you keep your concentrates sealed and in a cool dark place (cupboard, drawer etc) they should keep for well over a year without losing any potency. The only one I've heard that loses potency for some reason is CAP Sugar Cookie.
Like wine, beer and whisky, some are great off the bat....others improve with age, with some flavour profiles changing with the passage of time....some not for the good I may add.