Honestly I wouldn't even create thumbnails now that Data Bridge includes Image Resizer. Just upload the original image and resize and create thumbnails on the fly with Image Resizer. That would also mean that when you update and image you wouldn't have to worry about updating thumbnails at all. Another advantage is that if you update your design and decide you want smaller or larger thumbnails, or want a medium sized display you won't have to worry about updating images from the database.
Image Resizer is a superior solution to thumbnail creation and storage at the time of upload for a variety of reasons.
If you did want to keep with that technique, then you would have to re-create and update the thumbnails on the update page as well.
Did this help? Tips are appreciated...
