Form 114a is the authorization form.  The date your client signs the return does not equate to when the FBAR is filed.  In fact, if you take a look at Line 46 of FBAR, you will see that "[t]his date will auto-fill when the FBAR is electronically signed".  Even if you file it directly on the BSA website, you won't have to manually enter a date; it works exactly the same way.