Algorithm for determining if an HTC is present

[wraith-wireless]

ATT I have not seen any frames with the HTC present even though they are 802.11n frames. There is nothing I can find in the standards stating specifically how to positively identify when the HTC is present. If the HTC is parsed and it is not present then this will result in issues with layer 3 data and/or layer 2 encryption being parsed as HTC. Need to figure out either an algorithm that can identify frames with HTC or how to ensure that HTC is passed from the firmware?