This counts cells that the UPC policing function found to be out of contract but, rather than discarding outright, re-marked as lower priority, typically converting CLP0 to CLP1, so they'll be the first to be dropped elsewhere in the network if congestion occurs rather than being dropped immediately at this VC. An admin seeing this counter rise on a circuit knows the customer is exceeding their sustainable rate often enough to trigger tagging, a leading indicator that outright cell loss may follow if the trend worsens. For example, a circuit with a rapidly growing cktAtmInTaggedCells count but still-low cktAtmInDiscardedClp1Cells suggests the customer is currently being given the benefit of the doubt via tagging but is approaching the point where cells will start being dropped instead.