Sending Cleared alarms only to users that received the alert

Is there any way to send a cleared SMS alert to only the users that received the initial alert SMS?

At the moment I have a pipeline that sends SMS to a roster of users with a delay of 15 minutes between notifications to allow the user to acknowledge via return SMS before escalating to the next user in the roster.
Then I have a cleared pipeline that sends the cleared SMS to all users in the roster.
This is all working fine, however since this means that higher up the chain of escalation it is more possible that the user will just receive the cleared SMS, our customer has asked if it is possible to do either of the following:

  1. Only send the cleared to those who received the alert.

  2. Only send the cleared to the user who acknowledged the alert.

I’m not sure where to start with this or whether it is possible, so any advice would be much appreciated.