Yes, the RealTrack info of frozen tracks are saved in the SGU.
It will represent the time start/end in the source wav/wma, stretch and the transpose amount.
That's why you can change a frozen RealTrack to the same Direct Input track by changing the source wav/wma to the DI ones (temporarily then save track to wav).
If you knew what you were doing you could copy a section if a HEX editor of the bars of a saved frozen SGU and paste it into another,
then when you opened that frozen SGU it would have a new section of track.
It's the same if I drop a wav into Reaper, slice it up, change the pitch and rearrange it,
when I play it back it will still be playing the same original untouched source wav file.
The Reaper project file is still small, same like the SGU but just stores the wav start/end/pitch/stretch change info.

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