Sometimes campaigns may stop sending due to data not being up to date, a campaign being temporarily turned off, or a campaign pause being in place.
If you have not had continuous campaigns sending recently for any of the reasons mentioned above and the campaign(s) begin(s) sending again it will send to customers who would have previously been due for it within a certain time frame.
The "look back" period for continuous campaigns is 7-10 days so any customer who would have received the campaign in that time frame will receive it once the campaign is able to start sending again.
This does not apply to One Time or "Blast" style campaigns. One Time campaigns will only send to the customers shown on the Customer List at the time that the campaign is activated.
For example; If your data was not up to date for 3 or 4 days then your After Visit Follow Up Text will send out to the customers who should have received it during that time frame once your data is up to date.
If, however, you had a campaign pause in place for 2 weeks due to vacation then only the customers who would have received your campaigns over the last 7-10 days will be sent one once the campaign resume.
This also applies when activating a new continuous campaign. So, if you activate a new 2 Month Follow Up Text then it would send to everyone currently hitting 2 Months since their last visit AND anyone who reached the 2 Month mark over the last 7-10 days.
For more information on Continuous Campaigns please see Campaign Scheduler For Continuous Campaigns and Continuous Campaign Triggers