Originally Posted by Carpboy823

That means you had 20 rollover nights into 2017 (from 2016) as well. Nights will not roll over twice, so the calculation for the current year's rollover is (Total Nights) - (Rollover Last Year) - (Nights Needed for Status) = 115 - 20 - 75 = 20.

Originally Posted by CCIE_Flyer

The formula is posted at the top of this wiki thread. Likely you had rollover nights from 2016 that rolled into 2017, and those were (and always have been) backed out prior to arriving at your 2017 tally rolling into 2018. I'd bet you had 20 rollover nights starting 2017 - there's no "halving" type of calculus going on in the background.