Also, remember that most of the developer should be resplenished. Or you'll have to use starter.
No matter what, you should monitor the condition of the chemicals. For commercial use, you can use control strips to test. For personal use, print test strips with known good chemicals and the old chemicals to see if there is any difference.
For old chemicals, you should at least replenish 1/3 of the volume if they are more than 2 weeks.