if it is profile or lookup data, then yes it will be overwritten and only the latest values will be considered in audience qualification. but in data lake it will be an insert only. if it is event, then it will never be overwritten, not only from csv upload, from any source. --ssj

you can create folder in the audience page, and so the audiences can be organized based on the business unit. if different BU want to create similar audience, i would still think through to have different audiences for each BU as at any time 1 particular BU may want to change the condition which may...

refresh estimate wont behave the same way all the time. you need to wait for segment evaluation job to run to see the qualified profile count. --ssj