Place a contact multiple times to the list

Hello, I need your help.

I created a form and the contacts are subscribed to my list when this form is fulfilled .
When the contacts are placed in my list the sales team are trying to close the deal and sign up two year subsbscription with contacts who fulfilled the form and were placed in my list. The subscription expires every two years.
During these two years I will send a couple of emails to stay in touch with contacts who sign up a two year contract with us. So all the people who sign up are staying in my list.
After two years, when subscription expires, I will send a new form to them with intention of fulfill the form again. With fulfilling a new form, I want the contacts to be placed in my list again and the sales team will contact them again to sign up a new two year subscription. And so on and so on for every two years
And there is my question. We will send a new form to contacts who are already placed in my list. If the contacts who are already in my list will fulfill the form again how can they be placed in my list again if they have the same email as they had two years ago when they fulfilled a form and were placed in my list for the first time? I dont want to remove/erase them from my list beacause I want to send them emails to encourage them to fulfill the new form.

Thanks for your help and advice.

Hi Iztok, you could try using tags or custom fields to represent whether a contact has an active contract or not. That way, instead of re-subscribing them, which as you say, does not work, the form could add a tag that shows the contact now has an active contract again.