I would definitely check out our attribution feature, I think it is exactly what you are looking for. If you need a trial of the pro plan to test it out and see if it helps, we would be happy to hook you up, just reach out to sales - https://www.activecampaign.com/contact/
I create different tags for different forms. In the Form Action, I set it up to Add a Tag. Then i can simply use Manage Tags to view contacts based on tags.
I wanted to add some additional insights into this thread for anyone that comes across this post. You can now do one of the following to see which contacts submitted the form:
View Form Statistics and clicking “See Contacts” to see which contacts submitted the form (i.e. https://share.zight.com/nOu7B4xW). For more information on how to interpret form statistics, see our guide.
Segment contacts who “Submitted” the form like this: https://share.zight.com/mXuWoNOx to locate contacts who submitted the form.
Please don’t hesitate to reply back out or email us at help@activecampaign.com if you have any further questions.