My workflow is a lot of freezing tracks with effects on and dragging them to an audio track, but going back to a load of old tracks made in 10 and 11 many of the processed files are missing. Weirdly, most of their .asd files are still there. Being a suspicious person I don't let Ableton delete the files on exit as it sometimes prompts, and I would also hope that these internal files don't need the whole Collect All and Save process given they aren't imported but made by Live itself.
I'm baffled, and a bit sad that quite a few tracks are pretty much lost now.