I am using the get contacts by ID API https://developers.hubspot.com/docs/methods/contacts/get_contact to get the form submission, I have question does contacts api returns all the forms submitted by the contact Because in past couple of months I didn't see much increament in the volume of form submissions returned by the contacts api
Correct, this endpoint should return the total submissions along with the Id of the form that was submitted for the specific VID you're requesting the data for.
This is returned in the hs_calculated_form_submissions parameter in the response.