Every clinical trial paper I've read has a discussion of inclusion and exclusion criteria. I think for the trial to be registered, it has to include this information.
"unrelated reasons" should not be an acceptable excuse though. either state the reason or it goes into the trash. and if they were private reasons you can still contact them to confirm they left on their own volition and/or they didn't finish the trial without getting into specifics.
you only need one lie to suspect the whole thing