If you have data split across files that you want to merge (like your swim example), I’d use https://www.fitfiletools.com over GC.
Agree with @mcneese.chad I’ve never seen the same workout duplicated or merged together, only a single instance taken.
If you’re ever in any doubt or need help getting things to show how you want, reach out to support@trainerroad.com and they will sort you out. I once had a situation where I did 2 TR workouts back-to-back and I wanted them to show as a single workout, rather than 2 separate ones and they helped me out no problem.