Hi Kaitlyn,
To take it a step back, can you confirm there is a smart campaign in place that should have synced all of these records to SFDC? Recall that this doesn't happen on its own - records created in Marketo must be synced to SFDC via a smart campaign's flow step initially, then the record will continue to sync after that as updates occur. This smart campaign could either be:
- Centralized as part of an operational program, perhaps triggered by "Person Is Created" and containing a "Sync Person to SFDC" flow step, or
- Local to the marketing program, perhaps triggered by "Added to List" such as when event attendees are imported to a static list in the program to update program status and sync to the corresponding SFDC campaign via a "Change Status in SFDC Campaign" flow step.
Check whether there are any filters that could have excluded certain records from qualifying for the smart campaign(s).
Assuming such a campaign is in place to sync to SFDC, and these records were not excluded, we could also consider whether there might be a sync backlog. A list of <600 people on its own would certainly not lead to a backlog, but if there were any other major batch imports or updates happening in Marketo that would trigger the sync for tens of thousands of records, that could possibly delay the records getting over to SFDC. See this community post on Marketo / Salesforce Sync Limits & Priority Info for details.
Hope this gives you some ideas of what else to investigate if you aren't seeing any sync error notices in the campaign results or on the records' activity logs.
Cheers,
Beth Massura
2022 Adobe Marketo Champion