How do I tell the difference between beef stew that is overcooked vs. still needs more cooking?

Tonight, I simmered 2 lbs of chuck stew in water. After an hour it looked like it was dyed out.
The simmer was very gentle. Not at all a bubbling cauldron.
I probably should have simmered it much longer.
My questions is, how can you tell when your meat needs more simmering vs. you have simply overcooked it.
Update:
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