Installation confused about plugin location

The necessity was to have the files available in a new location. I kept the old ones “just in case”. As it turns out, IIRC the first time I could not get into the admin site at sitename/admin, I had to use sitename/wp/admin – so if I had deleted (“moved”) those files, I would have been SOL. However, the existence of files that are not referenced should mean nothing. WP had been told to look for them in a new location. Why should it matter if they are also present in an old location, or a dozen other locations that WP has been told NOT to use? It should not matter at all. If you are saying that was a mistake, and it led to the current behavior, for which there is still no explanation in sight, I would like to see some justification for that opinion. I still don’t see why WP should be attempting to update files in a location that is not referenced either in the database, or in any of the configuration files – or how it can know where the files are for the purpose of READING them, but not for the purpose of WRITING them. That makes no sense – so it must be incorrect, and a reference to that directory must still exist somewhere in the working image. However, the mere EXISTENCE of an old directory should have no effect whatsoever. If this is wrong, please explain how it can be wrong. Thanks for your help!