ComboBox populated in 2 ways and need to remove duplicate entries

Hi,

I am new here and an inexperienced programmer so please be gentle!

I have a userform comboBox which populates using unique values from a dynamic list in the worksheet and adds some additional items using .Additem. I have uploaded a sample of the workbook. I am currently working on the TypeComboBox in the BasicInformation userform. My problem is that once the .additem entries are selected by the user they end up in the same column which is being read by the combobox when looking for unique entries. Therefore the comboBox lists the entry twice as it is a unique entry in the column but is also added via the .additem. By way of an example I have inputted a sample entry selecting Architecture from the ComboBox. If you now add another record using supply chain vforum.xlsthe command button on the worksheet Architecture appears twice in the combobox in the userform.

I think there are a couple of options to solve the problem but I don't know how to write the code for either;
1. Once all of the entries are added (from both the worksheet column and the .additem values) add code which seeks to remove duplicates from the combined list in the comboBox.
2. Add the items from the worksheet column and then use code which says something like
if "blah" is not in combobox then .additem "blah"

I think the second option should be relatively simple but it has got me stumped. Any help will be greatly appreciated!

Thanks in advance!