Formula to add non-existing data into existing data

[SabbyJ]

Hi All,

I need help in pasting a set of data from File A to Masterlist. Let me explain the scenario

Masterlist Data
Company
A
B
E

Copy new data and paste into Masterlist
A
B
C
D
E

How do i add new data "C" and "D" into current existing data without changing data "A", "B", "E"? Since data will be in alphabetical order and i have thousands of data, is there any way to insert new data into existing data? Please help, thanks!!!