What if any is a good best practice / approach for a use case where a given business activity uses estimates that are then replaced by actual as they become available? In the same way that effective dates can be used to "automatically" (without user's having to know about it) retrieve historically accurate dimension rows, is there a similar way to have actual "automatically" replace the estimates without overwriting the data? I'd rather not have separate fact tables or columns and require that the users have to "know" about this and manually change it to get the latest actuals.
Why not have 2 measures in your fact table, one for estimate and one for actual? You could then have a View over the fact table with a single measure calculated as "if actual = 0 then estimate else actual".
Users who just need the current position can use the View; users who need the full picture can access the underlying fact table