List upload into engagement stream - question

Did you see any errors/failure message post the list import process? And, did you choose the Default list import mode while importing the list?

In case you'd chosen the default mode, and if you didn't see any errors, that'd mean that people would already have been in the DB, they'd have their data updated as per the data in the list import, given that the respective fields don’t have field updates blocked. FYR - Marketo dedupes based on the email address during list import. Also, importing a list in an engagement program won't add people to the stream, you'd need to add people to the engagement program's relevant stream using a flow step/or setup the trigger based transition rules at the stream level.