New field based on conditions of multiple existing fields

[gitguto]

Hi everyone,

Is there anyway to create a new field based on conditions of multiple existing fields?

I have two dimensions: {Version} and {Date} "MMDDYYYY". And one measure: {Units Sold}

My versions are: 'Historical' (with all the sales that happened), 'W1' (sales forecast from the first week of the year), 'W2' (sales forecast from the second week of the year), 'W3', 'W4', etc...

Every week,  a new version is uploaded in my database. 

I'd like to create a bar chart in which I could compare the evolution of these forecasts. (Just like the image below)

The problem is that the versions only contain data from the month they are uploaded forward. So when I compare the bars, they will get increasingly shorter. (Ex: W1 to W4 have data from Jan to Dec, W5 to W8 have data from Feb to Dec, W9 to W12 have data from Mar to Dec, and so on). I'd like to replace that missing months with the value in the Historical Version. 

I don't know how to do that, maybe in set analysis, maybe with a new calculated field, I've been trying without success. 

Thanks in advance for the attention.