Even if they got to it after going to a different page on the website. I would like to know if they came from google/facebook/etc. For this, you'd use a browser-side JS library that can store-and-forward UTM tags, known referrers, and other touchpoints from page to page, adding hidden form fields when a form is present. Ideally the library will maintain an internal trail of touches, so you can see both their first touch and their "conversion touch" separately. A robust example is Conversion Path from Romanoff Consulting, for which -- no big surprise! -- I provided engineering guidance. (It's a free library, but they also offer help w/implementation.)
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