Excel Table Appears to Automatically Expand but drop down list doesn't update

Hi Rhonda, the detailed steps as below:

1. select cells 'Device Type'!$A$1:$A$76  (you have done)
2. press Ctrl + T to turn it to table, and then check the box "My table has headers" (you have done)
3. select a cell of the table
4. select "Table Tools" tab in the Ribbon
5. change the table name to whatever you want (I make it as MyTable)
6. select "Formulas" tab in the Ribbon
7. click "Define Name"
8. give a name (I make it as MyList)
9. keep the scope as workbook
10. type the following formula in "Refers to"

    =MyTable[Column1]

    where "Column1" is the header, i.e. the content in your workbook 'Device Type'!$A$1
11. select the cell that you want to use Data Validation
12. select "Data" tab in the Ribbon
13. click "Data Validation"
14. in the "Settings" tab, select "List" for the dropdown box of "Allow"
15. in the textbox of "Source", type the following

    =MyList

16. Try to insert items in your table, and test if it is reflected in the dropdown list

I am sorry about the previous reply.  I was trying to explain more about what Excel is "treating" the insertion that you made.  Again, sorry.  Please try the steps above to see if it is what you expected.