To prevent abuse Formspree treats each combination of URL and email address as a different form. Each different form must be confirmed individually. So if you have your form appearing on https://your-site.com/contact and https://your-site.com/contact.html, these are different forms and must be confirmed separately. The same if you have https://www.your-site.com/contact.
If you want to avoid that trouble, or if you have dynamic pages being generated in your site, the way to do it is to create a Sitewide form on the dashboard. After placing a verification file in the root of your domain you'll never be required to confirm it again. This is a feature available for Formspree Gold users.
If you happened to lose the content of some submissions because of this, we are sorry but that's a sad thing that can't be fixed.