Methods and systems are disclosed to embed valid-field (VF) bits into classification keys for network packet frames. The embedded VF bits allow for extracted data from existing fields associated with frame data to be distinguished from default data used for missing fields where this extracted data and default data has been included within a frame classification key generated for a network packet frame. In certain embodiments, a valid-field field extraction command (VF-FEC) causes a key generator to embed VF bits into a frame classification key, and the logic state of the VF bits are used to distinguish extracted data from default data. Further, the disclosed embodiments allow VF bits to be selectively cleared based upon a bit mask applied prior to embedding of the VF bits. Still further, users can define VF-FECs and other field extraction commands (FECs) for key generation through one or more programmable key composition rules.