Dynamic dropdown of unique values

Question

I want to put a dropdown in B20, where the options are a list of unique values from another tab.
This formula outputs the correct values to another range =Sort(Unique('Raw data'!E2:E)) but I don't actually need them to be output. I added it as a custom formula in the Data Validation dialog, but now how do I make it a dropdown? There doesn't seem to be an option.

I can output the values to a new range e.g. A1:A10 on another tab and then use that range as the source for my dropdown. 
The problem is that as my raw data changes, new unique values may appear and I will need them to appear as options in the dropdown list. So next week the range might be A1:A15, or maybe only A1:A8
How can I make the range dynamic? Or better yet, how can I make the formula above (which is correct) operate as a dropdown?
Thanks

Spencer Farris · Accepted Answer

You cannot use the formula itself as the dropdown criteria: it must be used on the spreadsheet and the point the dropdown at the range. But you can point it at a bigger range and it will bring in all values in that range, and nothing for the blanks. So normally I point it at an open-ended range A:A or A2:A if there is a header.