The disclosure relates to digital watermarking, steganography, and specifically to message coding protocols used in conjunction with digital watermarking and steganographic encoding/decoding and payload interpretation methods. One claim recites a method for interpreting a data structure having fixed and variable message portions, the method comprising: processing the fixed message portion to determine a version of the variable message portion; decoding the entire payload field of the variable message portion according to the determined version; and interpreting only a portion of the decoded payload field according to the determined version. Of course, other features and claims are provided too.