Help BackFilling Time Series Data from Economic Scenario

[nshapir2]

I have time series data that is organized by scenario, projection month and return for a fiew equities. 

My data is for months 1 to 360. I want to create a row called Month 0 (it would just be a value of 0) and then backfill the equity values such that the value for each equity or treasury is equal to the time 1 value.

[AZuc]

@nshapir2 

Could you provide a sample of data with the expected result?