idle vs n/a utilization

Hi
For some kernels, I see memory utilization is said to be idle while for some others the reported value is n/a. Are these two have the same meaning as zero utilization also known as memory unit not being used? If yes, why not reporting 0 instead of idle or n/a?

For a kernel, I see:
Avg. duration = 1.7 ms
System memory read utilization = idle
System memory write utilization = 1
Shared memory utilization = idle
L2 cache utilization = 2

For another kernel, I see:
Avg. duration = 6.7 s
System memory read utilization = 1
System memory write utilization = 1
Shared memory utilization = n/a
L2 cache utilization = n/a

Are these values normal?