Transferring books to CC using a cabled connection has never worked, with two exceptions:
- If you transfer epubs to CC's epub storage folder using a cable then subsequently connect as a wireless device, CC will attempt to match the books to the calibre library. This usually works if the books were transferred using calibre's send-to-(folder-)device or save-to-disk commands. It usually does not work if the books are simply copied from calibre's storage folders. It almost never works for books other than epubs. See the FAQ I have books on my device that don’t show up in CC. How do I fix this? for more information.
- If you transfer a complete calibre library including the metadata.db file to the device then you can use CC's "Local cloud connection" to open that library and copy books to the local CC library. See the FAQ [Android] I have a copy of a calibre library on an SD card. Can CC use it? for more information.