Yes, there's lots threads about this both here and on Flyertalk.
Say you stay 90 nights in 2014, youll rollover 15 (90-75=15) to 2015.
If you then stay 65 nights in 2015, you'll retain plat for 2016 even though you've not managed to stay the required 75 nights because with 2014s 15 rollover nights your counter will show a total of 80. But you'll have nothing to rollover to 2016 as rollover nights cant rollover twice and hence the 15 nights from 2014 don't count for 2016 rollover.
Look over How to Calculate Rollover Nights for some examples. Like the replies above have suggested, the most likely reason you have 0 nights to start the year is due to expiring rollover nights from 2014. Unfortunately since they've disappeared from your "nights" count, the only way to know for sure would be to call customers service.