I think although their website says 23 weeks from October 15th, their hard deadline is March 31st. Also interesting to see they updated their "Notification of Decision" blurb - not sure why they changed "March 31st" to "end of March" though, I think that just adds unnecessary uncertainty.
2016's blurb: NSERC notifies applicants whose applications were submitted to NSERC of the results by mail by March 31. NSERC will not provide results by telephone or email.
2017's blurb: NSERC notifies applicants whose applications were submitted to NSERC of the results by the end of March. NSERC will not provide results by telephone.