DAX Formulas Advice Needed for YoY Growth/Sell-through etc

Hello!

Not sure if this is the right thread for this topic so if it's not please let me know .

I have started to use Power Query/Power Pivot and because of that I need to start to use DAX expressions and formulas. I work for a retailer and need to just need to start with some basic calculations like Year over year sales growth or decline.

However, using DAX expressions to build calculated formulas in my power pivot tables has really stumped me and I've hit a road block. In original pivot tables, the formulas are very easy as can just work with the fields in the data table but DAX expressions are stumping me.

In our business, we work in week chunks and that is how the data is posted. For example, week 1/2019 is shown as --> 1.2019. So the sales or store inventory data is not shown by a specific date (ex. 01/01/2019). Most of the online help in articles/youtube videos etc has shown this same situation but it almost always refers to data that is in the date format of specific days and not weeks the way my company provides the date. A general question, can I still build a DAX expression for YoY growth if our timelines are shown like this?


I've attached an example of the data source that I am using, it's only a few lines but you can see generally how the data source is laid out. I've also attached screen shots of my power query and the power pivot tables that I've created.


Thank a lot for your help!