Does check marking "Add existing contacts to Constant Contact" mean that any existing prior submissions in the form will be added to constant contact?

Does check marking "Add existing contacts to Constant Contact" mean that any existing prior submissions in the form will be added to constant contact?

That is correct, existing submissions should be sent to Constant Contact and contacts should be created out of them.

Let us know if you have any further questions.

Thank you!

so i should uncheck it if i don't want any past submissions in that specific jotform form to be sent to constant contact correct? I am only interested in future submissions to be sent to constant contact and unchecking that option should not affect it 

Yes if you uncheck all the previous contacts in previous submissions made will not be added.