Because RADIUS accounting doesn't normally involve a challenge-response exchange the way authentication does, a nonzero value on this accounting-table counter is anomalous and would point to something unusual on the accounting server's side, rather than reflecting a real design feature of the accounting protocol, unlike its meaningful counterpart on the authentication table. For example, this counter staying at exactly zero over the device's entire uptime would be the expected, healthy result for a well-behaved accounting server.