Usually for my succulents, rotting at the base of the plant serves as a warning that it may already be rotting due to too much water.
Wrinkly leaves can also be due to damage by insects. And sometimes the signs of overwatering is similar to underwatering. I always try to feel the soil, if it looks damp, don't water. Or sometimes when I have put stones on top of the soil, if I look under it and see the soil is still damp, I do not water. Jade plants are toughies.
