Muriatic acid doesn't degrade with time . . . but bottles do. Be careful to set things up, so that if the bottle shatters, you are protected (glasses, gloves, running hose!)

If it's still in a box, move the box OUTSIDE before opening it. If you have a large enough plastic bucket, put one gallon in the bucket -- gently! -- and then poke it with a not-sharp stick, to see if the bottle is brittle. If the bottle is OK, proceed.

Be SURE to store the bottles so sunlight does NOT reach them.