Recently a customers asked about getting historic data into Google Analytics:
I'd love to know how to get Shopify data (prior to embedding Google tracking code) on to Google Analytics to see previous years data.
At first I didn't think that was possible but after a bit of searching I found Google's Data Import that supports adding that data and other data.
It'll probably be a significant project getting all of that data correct, but for important data it might be worthwhile.
One useful thing about Repeat Customer Insights is that it'll import all of your order and customer history automatically. That full history makes the results from its algorithms more useful and gives you a clearer picture on your customers.
Use cohorts to find out who the best customers are in your Shopify store
Repeat Customer Insights will automatically group your customers into cohorts based on when they first purchased. This will let you see how the date customers bought would impact their behavior.