Here is what the NNP says about retro:

Hourly pay rate increases will take effect as shown in Section 3 Compensation. The consolidation payment (mid-month paycheck) on December 15, which is for November flying, will be paid at the prior hourly pay rate. On or about December 16, each pilot will receive a retro payment for all hours paid from January through November of 2016. The end-of-month partial payment on December 30 will paid be at the new hourly pay rates.

Denny