Usually emperors were very careful to pay the army in good coin. Troops got cranky when paid in debased money. Ordinary folks used copper coins with a silver wash that made them look silverish, but nobody was fooled—kind of like our coins after 1964—the coins by this time had no intrinsic value.
Earlier emperors, like Nero issued silver-covered copper coins that had to be accepted at their weight’s value, but refused these same coins when used to pay taxes.
Your post is an example of why FR is crucial from a historical perspective.