wheat futures zw rollover date

[easyfying]

from cme website the last traded date is always the business day prior to the 15th calendar day of the contract month.
however when i goto ninjatrader instruments and check rollover dates for zw wheat futures they are all on dates 23rd or 24th of the month prior to the the expiry month.please explain why rollover dates are almost three weeks prior to the last trading day for the contract.its bit confusing because normally for all instruments rollover date is two or three days prior to last trading day of contact.

[NinjaTrader_Jason]

Hello easyfying,

The rollover date is when most traders rollover to the next expiry month. The ZW 05-15 uses 2/23/2015 as rollover date. You can see in the attached screenshot that most traders rolled over to the 05-15 expiry on 2/23/2015.