Media files not showing over at the new wordpress site

I had a WP site up and running for years at one host, and decided to change hosts and develop a new site while I was at it. I did several things to populate the new site with my files/images. I exported the SQL, and then imported that to the new site; that seemed to work just fine; for my pages and image files, etc., I did an FTP download to my computer, and then an FTP upload to my new site. That would have included /images/uploads. Afterwards, I change to a new WP theme. But the only things showing in my media library are images that I uploaded to this new site, directly by uploading. The other images don’t show up. However, talking with my host, the images in on their server, but my WP structure is not seeing them. Any ideas how I can simply fix this? I say simply because I am not a web developer, I’m just someone who thought she knew how to do this – and it all worked, except for this tiny glitch. I have hundreds of images that are on their server. I could possibly try to upload one of them that it technically already there; would I get a message saying that it’s already there? Or because it’s an upload on a different year/month/day, would it be treated like a new file?

Many of these pictures are attached to blog posts that I don’t want to mess up; hence my concern about how to get the current site to recognize that they are uploaded on the server…host is looking into this as well.