Whenever you start marketing to customer segments you should use different UTM or other tracking codes to be able to track each campaign separately.
Some systems like Repeat Customer Insights can work out their purchases without a tracking code but many systems cannot and could attribute those sales as new customer sales. Especially if it’s been awhile since they’ve visited your store or have switched devices (i.e. cookies can get lost or expire).
Adding a UTM code is easy and is used automatically by Google Analytics to give proper attribution to your segmenting campaign. Other analytics systems might use other codes but I’ve seen quite a few support Google’s UTM anyways.
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.