How to send existing subscribers who haven't received welcome series

Hello @3000month2021,

If you haven’t already, I would encourage you taking a look at our How to Back-Populate a Flow Help Center article. In it, you’ll find a helpful video tutorial that walks you step-by-step on how to backpopulate a flow! It even explains the difference between the two Schedule Relative to When Recipient Was Added and Schedule Relative to When You Back-Populate options for list triggered flows.

One other thing to note is if you’ve backpopulated a flow incorrectly such as initiating it when the emails were in draft, using the Schedule Relative to When Recipient Was Added option if the contacts were added to the list longer than the time delays in the flow, etc.; this would technically have initiated those contacts into the flow. This means that any subsequent backpopulations would not re-queue those users up for the flow as they would been considered as completed the flow already. If this occurs, we recommend cloning the flow, making the correct adjustments, and backpopulating the newly cloned flow.

I hope this helps!

David