Hi,
I'm not completely sure what you are trying to accomplish.
In v6 you actually can send a mail to all subscribers, wether they received it before or not. When you resend your campaign on the summary tab you can select if it should be send to new subscribers only or to everybody on the list.

Also, in Automations you can send mail to your entire list regardsless of the subscription date. You probably have used the subscription date as a filter. If you need further assistance with your automation, please tell us more detailed what you want to accomplish and add the settings the of youyr Automation as shown in the summary tab.