the hidden info is in the registry, i’m not sure you can do anything now but before you install a new trial backup your registry then install the trial, and after you uninstall it restore your registry (don’t install anything else during the trial or you may have to reinstall it after you restore your registry)
If you know the name of the program you want to remove you can go in the registry and search the key names and manually delete them. Please note you can mess your registry up in turn messing up windows if you delete the wrong key. Programs also leave files behind after you uninstall them, simply go to the intallation location and delete them.
Yup, the registry is the place where they leave their have crap. If you install lots and lots of shareware programs, your registry will have lots of crap entries, which adds to the fundamental problem of the registry as well.