Hi @Dominic Zijlstra41 Can you confirmed if the Sequence (Step A) subscribers is added to a certain tag or not?
What I'm thinking is, if these subs are added to a tag we can create conditional filtering and add jump event to skip the sequence if they have this tag already. For example in this automation I created. If subs has 'tag t1' and they are exclusively added because of the email sequence (Step A) they will move forward to the Sequence (Step B).
https://forms.convertkit.com/a/e71981b50550
Then if they do not have 'tag t1' they will exit the automation.
About exclusion. You can exclude tag in each email in sequence or in general settings.

Or in your sequence general settings:
