Entered here for prosperity and so I don't have to search for this ever again.
The MIFARE DESFire Application Identifier (AID) is a 3-byte value that represents the application ID used for RFID functionality that holds files. This can be a MIFARE Classic AID structure (2 bytes) adapted for use with the expanded MIFARE DESFire AID (3 bytes).
https://www.nxp.com/docs/en/application-note/AN10787.pdf
A 2-byte MIFARE Classic AID adapted to MIFARE DESFire uses a leading nibble of 0xf and a trailing nibble of 0x0 - 0xf. The middle 2 bytes are the MIFARE Classic AID. ex., 0x7009 is the Timelox AB MIFARE Classic AID; 0xf7009x is the adapted AID for MIFARE DESFire.