There is a discussion of this, I think, in the Classic Pronto Forum where you basically have to learn 2 versions of the code and then append the IR code data together. There may be other ways around this. Eigeny (Eugene) Eulanov, once upon a time knew all the in's and out's of the Classic Pronto Firmware and wrote a document that is published alongside Barry's Classic Pronto Hex Format document in the Classic Pronto Files-User Documentation subsection.

Not sure if any of this will help but it is what I can offer.