Mix a 10% solution of Benzotriazole and start by adding say 10ml to your working developer and you'll find that it will increase the contrast of the old papers that you've decided not to throw away (wise man, this from the world's best! hoarder)

The benzotriazole will also cool down the final print colour. I sometimes use this little dodge to increase the contrast of a current paper if I need to when I have a very low contrast negative and have failed to print the contrast I wish even with a number 5 filter or the hardest single graded paper.