A fair question! As long as the filenames will be the same as before you shouldn't run the risk of doubling up, as the books and thumbnails should be overwritten.
The filename on the Sony will depend on 2 things: your 'Save template' (same Prefs page as before) and whether you've changed any of the metadata included in the template, since the initial send.
There is another option you could try which doesn't involve resending any books. You could:
- Make sure that Prefs - Sending books to devices - Metadata management is set to Automatic
- Reopen the Prefs Device plugin page (used in all the previous posts) and check the box labeled 'Refresh separate covers when using automatic management'
- Connect the Sony to Calibre in the normal way and let it do its processing (may take a while with this option set)
- When it's finished, do nothing more than disconnect in the normal way
- Calibre should have re-synched the thumbnails of every book it knows about on the Sony.
- Uncheck the box you checked in step 2.
If this process took very little time you could consider leaving this box checked permanently. However, if you have a lot of books on the Sony it will slow down the process every time you connect to Calibre. Personally, I use this box as a temporary setting for one connection only then I reset it to unchecked after disconnecting. It's a good way of getting all your book thumbnails up-to-date if you've made a lot of cover changes in Calibre. This method should not risk interfering with any bookmarks or notes you may have already made to existing books on the Sony. So you could consider it 'safer but slower'.