Data Validation - With Exception?

[cmarie85]

Hello! Tried finding a response in these threads but no such luck.

I don't know if this is possible but basically, I currently have this data validation set:
=COUNTIF($E$1:$E$10001,E1)=1
So that no repeating data can be put into a single column. However, I need to make an exception for "n/a" to be able to be repeated.

To explain:
I track incidents called RCCL, SAMP and MONIs for my agency. RCCLs have Investigation numbers. But SAMPs and MONIs don't.
So I need to be able to put in an Investigation # in the "Invest #" column but instantly know if it's a duplicate number because this means it's an incident i've already entered.
But I also need to be able to put "n/a" multiple times, in cases that it's not RCCL and instead is SAMP or MONI.

Any help would be greatly appreciated!

Here's a snippet:

 

[jasonb75]

It should work with a basic OR condition like

=OR(COUNTIF($E$1:$E$10001,E1)=1,E1="n/a")

You could add another condition to ensure that n/a is not entered against RCCL if that is necessary.

 

[cmarie85]

Worked perfectly! Thank you so much! ?