Bitdefender offers large update file packages for offline systems : https://www.bitdefender.com/site/view/Desktop-Products-Updates.html
It would better for Bitdefender to offer an updater that downloads virus definition updates incrementally to a drive, external HDD or a pen drive (and also Bitdefender program updates, if the user desires so).
Bitdefender can also use such an updater to collect information about illegal/pirated Bitdefender installations that are being used offline only.
Avira and Kaspersky have this type of offline updater for their products. It helps to save greatly on time and a user's data plans.
