I have a suspicion that Bailey's and others similar go off even unopened (I think I remember that happening to me years ago) because the cream goes rancid.
Baileys is the only cream liqueur that guarantees its taste for 2 years from the day it was made, opened or unopened, stored in the fridge or not when stored away from direct sunlight at a temperature range of 0-25 degrees centigrade.
One of the keys to achieving this 2 year shelf-life is in our unique process of blending of fresh Irish cream with the spirits and the whiskey without the use of preservatives. The alcohol acts as a natural preservative for the product.
Under normal conditions of storage Baileys has a shelf-life of 24 months.
If you are concerned about a bottle of Baileys please check the Best Taste Before date on the bottle - all bottles carry a Best Taste Before date. This number is located on the bottom left hand side of the back label. Example : Code 11 20XY would mean that we guarantee the product would taste perfect until November20XY (XY is the year 2 years from the date of manufacture)."
1/2 pt single cream
1/2 pint whisky
2 eggs
large tin condensed milk ie, Nestles, NOT Carnation type
spoonful of cocoa for colouring
Liquidise it, test it, bottle it, test it again.
I've drunk it 2 years after making it with no ill effect, although the cocoa does tend to settle at the bottom.