I have learned from experience.
Open a file in RealBand or PowerTracks that I want to save, then save it right away as a SEQ file (look at the file type when saving).
Once a SEQ file, it will always save as a SEQ file unless you tell it to save as something else.
If you want to save anything on a track; anything to do with effects; any audio content that you want to work with later, save it as a SEQ file.
It's great that you can save certain parts of your SEQ file as a different format, but only the SEQ file will give you everything. Start there, and you should have no problem with losing any content upon re-opening the file. Oh, and save often.
To me, SEQ file = RealBand/Powertracks. The other formats are just capabilities within for when you need it (save to a MIDI, which will only give you the MIDI data; save to SGU/MGU, which will give you the chords and style, along with maybe a melody track, but little else; save to WAV will only give you a single WAV file that can't be split out again).
Oh, and did I say, save often!
