Looker Data Studio - Inventory and Past sales data blend

We have developed a looker studio dashboard that allows users to view past sales based on their location based on Customer, Year and Product sales from 2020 to the current year.

As well as helping with improving customer retention, it is used to help forecast based on previous years' sales history.

As part of an improvement process, we are looking to blend the past sales data with an additional data set that shows the current and on-order inventory of products along with the previous sales data.

The data sets are housed in Google Sheets and updated on a daily basis.

The Customer, Location and Product codes are unique to all data sets. The current inventory data may include products that have not been available in the past, however, a data blend should be able to display this data without the presence of previous sales either at the location to customer level.

The data is operational and two separate. Dashboards, but the function is not operating as expected in the blend. I require assistance to review the process and correct it. There is also more work on this and other looker projects I am currently running if there is interest in continuing to work together.