Stealing Something That Later Increased in Value

In america if you stole something like bitcoin or stocks or a physical coin collection and at the time it was only worth a few dollars but later increased in value by the thousands would that change the severity of the crime? How would a statute of limitations apply? What if the thief held onto the bitcoin and sold it after the price increased? Or what if the thief never sold the coins? Does the thief have to return the exact number of coins or does he have to return the value of what he stole at the time? What if he stole something worth x amount and it later decreased in value?

Stealing Something That Later Increased in Value