Almost no one uses CRC with SdFat so the table and function are not loaded by default.
If you want to use CRC with SdFat and in your app, do what I told you above - remove the static declaration and share the table and function.
You can easily do this and since there is no other user interest, it's not worth making sharing CRC a feature of SdFat. I get almost daily requests like this and I just can't add bloat for every user's request.