bcat is just a download of all available gifts that can possibly be redeemed at a given moment in time; some may be obtainable only if you have a valid serial code, or others may be inaccessible until a later reveal. Gifts that expire/ are no longer distributed... are no longer distributed in bcat, and are thus removed from your local storage. Hence why there's the need to archive here to preserve previous content gifts.
Since all gifts as of late require a serial code, you have to enter it in and the online server will say "go ahead, load the contents from folder X and give that gift". The server knows the current bcat folder structure, and there's no way to desynchronize it because you have to be synchronized to enter in a serial code.