This counts instances where a PDU's source address was not found in the switch's address table for this interface, meaning the sender is not recognized as a valid, provisioned SMDS subscriber on this port. An admin treats a rising count here as either a provisioning gap, a legitimate new customer address not yet added, or a potential unauthorized or spoofed source trying to inject traffic. For example, if a customer just added a new source address on their end without notifying the carrier to provision it, their legitimate traffic would start incrementing lportSmdsCntSaNotFounds until the address table is updated.