Hopefully I can explain this easily.
We have Marketo and SFDC sync'd up and have found that SFDC cannot update a lead once converted, therefore we need to make sure all the contacts that are merged over to the account will have a field change and overwrite the field on the lead with the information on the account. We are finding that Accounts and Contacts are not syncing with the same information until they are converted which means creating Smart Lists is pulling in missing data/contacts.
How can we automate this? We are doing batch runs weekly to clean up the fields but it is taking too much time.