The ideal flow is for Marketo to capture all of the lead info (form fill data) and then pass it to SFDC. You should be creating the event as it's own program in Marketo and then sycn that over to SFDC. Sounds like you are doing the reverse. if you are not using a marketo form, I assume AEM has a marketo integration where it can automate the forms to be linked to a marketo program and have leads flow through the program into SFDC. Several event management platforms such as Splashthat have marketo integration and can automate data flow into marketo.
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