Licensing for social media use

We have received a copyright warning from Facebook. We often produced items for clients and in those instances we download a separate license for each client. If they get a copyright notice then we provide them with the license and they dispute it - no problems. In this instance, however, we created a video for ourselves and send it out to our client list. Now I am concerned we need to download a license for each client, though the video was not created for that client it was created for us. Can we get some direction on the correct way to handle this?