I'm familiar with this promo from the Seven Stars Insider. The multiplier only applies to base TCs earned (RCs are irrelevant in this conversation) and not to tier bonuses. It also won't do anything for someone needing these on their 2018 TC count as it takes 5 business days after 12/27 for them to post. It's been confirmed that it'll be added to your 2019 TC count which resets to 0 on 1/1/2019.