Caching issue?

We had an old site that was on multisite and we created a new site that isn’t multisite. There were some files saved in multisite that we are redirecting to the new site.

For example, we had a link such as: https://www.mysite.com/subdirectory/wp-content/uploads/sites/4/2015/11/Resource-Guide.pdf on the multisite. In order to preserve the files we created a new directory on the server such as: https://www.mysite.com/subdirectory2/wp-content/uploads/sites/4/2015/11/ (We couldn’t use /subdirectory/ because there is a page with that url).

So now, I have a redirect set up that is: https://www.mysite.com/subdirectory/wp-content/uploads/sites/4/2015/11/Resource-Guide.pdf >>> https://www.mysite.com/subdirectory2/wp-content/uploads/sites/4/2015/11/Resource-Guide.pdf – It seems to be working for me, but our users are getting a 404.

Any ideas? Maybe the old url is cached in their browser? How can I get around this?