Creating customer with duplicate code

I have few customers that the first 3 letters of the Company are the same. We have decided to make our customer codes the first 3 letter of company name then 001, 002 and so on.

The result is that we now have duplicate codes and manually now change them to 002 and so on. The challenge is that we have long list and only realise the duplicate codes when we start invoicing.

Can you add a function that Manager can warns you that codes under customer and other modules are duplicate or already in use?