For most of the reagents it is fine. There are a few that have a short shelf life and the R-0871 is one of them and it is not a bad idea to replace this one yearly. It can be oxidized by exposure to air, particularly in a partially filled bottle. If it has a pink or orange cast it needs to be tossed out and replaced. DPD powder also has a shorter shelf life and is very sensitive to heat and humidity but as long as it has not turned completely black and can still form a pink color it is usable.