How long does latex paint last?
From what I have read it varies with the quality of the paint and the storage conditions,but 3-5 years is reasonable for unopened cans. Most of the evidence seems anecdotal. There always seems to be a case of someone using something 20 years old that they got for free and it lasted 30 years. There doesn't seem to be hard evidence from manufacturers saying that you will decrease service life by X number of years if stored for X number of months.I would do a test sample on something similar to your planned use, wood trim,drywall etc. Give it a day or so to see how the color match and texture looks. If it looks OK you have nothing to loose. If you buy new paint you will probable want to redo the whole wall so it will blend in. If the old paint doesn't match you'll have to redo the wall anyway