Checking Numbers Between Columns

[Nanaia]

I'm trying to check the first four numbers found in column A and see if they are located anywhere in column O. I've tried VLOOKUP with LEFT but cannot seem to get the it to work. It always results in an #NA error. My goal is; if the first four numbers is not found anywhere in column O, I would like the result of the formula to display the numbers that were not found in column O. i.e. if column A has 1234 as the first four numbers and it is not found anywhere in column O, the result of the formula should display 1234.

This is the formula I've tried
[ =VLOOKUP(VALUE(LEFT(A2,4)),LEFT($O$2:$O$500,4),2,FALSE) ]

Thank you in advance for your assistance.

 

[Nanaia]

Here is a link of the part of the file I'm working on. If the site will allow me to share it...

https://www.dropbox.com/s/g7kqjjuw9fvrbsn/P4 PROG.xlsx?dl=0

The end goal is to have every column with the same program file names, focusing on the first four numbers of the file name. I've made column A the master list and as I'm going through the other columns and find a file name not in the master list, I create the program and add the new file name to the master list. What I'm trying to do in the table to the right is compare all other columns/categories against the master list and have it tell me which files need to be created for each category.

 

[Fluff]

If I understand correctly, try
=IF(ISERROR(VLOOKUP(LEFT(B2,4),LEFT($A$2:$A$1001,4),1,FALSE)),B2,"")

 

[Nanaia]

It's always a delight to try to explain Excel.
If at first you don't succeed...
Looking at the formula in column X; this compares column A to column H and tells me what files I need to create for category V (the files listed in column H). So I'm looking at column A, and whatever is listed in column A and not in column H I want the formula to tell me by listing at least the first four digits of the file name that's missing.

 

[Fluff]

As I do not have the time to go through almost 400 rows of data & manually compare it to other columns of data, can you please explain what is not working & give examples?