I have managed to create a report showing to original medium of our leads created and it's shown some interesting numbers.
One thing that has appeared is comparing cookie value parameter and original referrer. We have added an "original lead medium" to our forms capturing the cookie value - this field cannot be overridden once created. The value we have capture is the utm_medium from our cookie value for example "email". Looking through the leads with this value I am also seeing original referrer value of google in a number of cases.
In this example can we assume was the first touch point? Was it
a) The lead received an email - thus being cookied, then went on to google to find out who we are, then completed form
or b) previously had found us on google then received an email forwarded to them before completing a form