I had originally posted this because I was seeing duplicate tag names - only one of which was being displayed by exiftool using commands such as:
exiftool -a -G1 <filename>
after more research i see the following code:
0x100b => { #2
Name => 'NoiseReduction',
Flags => 'PrintHex',
Writable => 'int16u',
RawConv => '$val == 0x100 ? undef : $val',
PrintConv => {
0x40 => 'Low',
0x80 => 'Normal',
0x100 => 'n/a', #PH (NC) (all X100 samples)
},
},
I'm assuming that this means that even though the tag exists it won't display if the value is 0x100.
I hadn't been aware that exiftool sometime skips tags and doesn't display them