2016 Safe Harbor Contribution missed

A calendar year plan still hasn't deposited its Safe Harbor Non-elective for 2016. The operational failure can be Self Corrected as long as it's done within the Correction Period. Regs say the Correction Period starts the year after the failure occurred......but in this case, did the failure occur in 2016 (the year the contribution is for), or 2017 (12/31/17 was the latest the contribution would have been considered timely)?

Thanks

I believe your failure occurred in 2016.