Overtraining a specific muscle is basically the condition of causing excessive microtrauma and fatigue. A major symptom of this is substantial restriction of range of motion.
Overtraining in the traditional sense of the word (most common) is a condition of overworking the CNS, symptoms of this are lethargy, tiredness and overall feeling shitty.
If you feel that your shoulders are good to go, then there's no real probem with working them again.