Although it's technically possible, different data sets should not be uploaded onto the same engagement. The reason is that every new upload overwrites the previous one, so, only the last upload will be visible on the portal.
One engagement should be created for each data set that needs to be uploaded. Click here for more details about creating multiple engagements for one SME Contact.
REMEMBER: On one engagement, a database can be uploaded multiple times in the day/week/month/... , as much as your engagement progress requires it.
Please note that if multiple engagements are created for an SME Contact, they will see all these engagements on the portal after signing-up. They will not have to sign-up for each engagement separately.